So, to achieve above objective every chemical process industry must be energy efficient to minimize their carbon foot prints. Moreover, need to reduce the effluent generation during chemical manufacturing. This we can achieve by adopting zero discharge policy, be it for any type of effluent. However, as a chemical manufacturer selection of a technology is very important, where effluent generation is minimum. Also, selection of effluent treatment methodology is equally important to make the manufacturing facility zero effluent discharge. In this article we will discuss various types of common effluents generation during chemical manufacturing and their possible treatment methods.

Various Types of Effluents Generation

We can broadly categorize the effluent or waste generated in chemical manufacturing in four types as below:

1. Liquid Waste – This can be of different type based on chemical compositions present in water. Like Aqueous effluent containing acid impurities like HCl, H2SO4, HNO3, etc. Other can be Aqueous effluent containing organic impurities such as benzene, ethanol, acetic acid, pyridine, etc.  Apart from this Aqueous waste having impurities of various salts like NaCl, Na2SO4, MgCl2, NH4Cl, etc. Other types can be the various combination or mixture of above effluents. The sources of these wastes, can be the processes like extraction, decantation, centrifuge or ANF washing mother liquor, neutralization, etc.
2. Organic Waste – This is also in liquid form but in some cases at lower temperature can be solidified also. An organic residue is mix of high boiling organic compounds or contain tarry material. In chemical industries organic residue mainly generates from the bottom of a distillation column.
3. Solid Waste – It can be semi-solid also like slurry or wet cake containing moisture or other chemical in the range of 5% to 30%. The examples of solid waste are activate carbon, reactor catalyst, inorganic salts (i.e., NaCl, MgCl2, Na2SO4, etc.). The final discharge points for these wastes are solid-liquid filters, sedimentation tanks, centrifuge, ANF, ATFD, etc.
4. Gaseous Effluent – The source of this effluent stream in chemical plant we can see from absorber column top, spray dryers, vents of heat exchangers, vessels and tanks. Many times, this effluent is not harmful for the environment and we can discharge it into the atmosphere without any treatment. But in some cases where it contains chemicals such as ammonia, organic solvent, reactor off gases mixture of various toxic organics, it requires treatment before venting into the atmosphere.

Effluent Treatment Methodologies

We select effluent treatment methodology based on the type and characteristics of the effluent. Below are some common techniques to treat the effluents in our industries:

Liquid Waste Incinerator

This incinerator we use to treat the aqueous waste containing organic impurities, which are not biodegradable and we can not treat this using ETP. As we can not discharge or recycle the waste water due presence of hazardous chemicals in it. Therefore, for treatment of such effluents we use incinerator.

In Liquid waste incinerator there is a combustion chamber which operates around at 800 to 850 ⁰C temperature. In case of the presence of chloride impurities in waste water we need a secondary combustion chamber also. This secondary combustion chamber operates at around 1100 to 1150 ⁰C temperature to incinerate chloride chemicals. The fuel inside the incinerator can be furnace oil or natural gas. Hot flue gases subsequently pass through a waste heat boiler and we can generate waste steam, which we can used inside the plant. After waste heat boiler flue gas passes through economizer where combustion air required for incinerator is preheated and flue gas passes through chemical scrubber to remove the NOx and SOx impurities before discharging into the atmosphere at safe location.

We use liquid waste incinerator for the incineration of Liquid Organic Waste and Vent Gas also. As organic waste and vent gas has good calorific values, therefore it reduces overall fuel consumption for the incinerator. Below is the schematic sketch of a Liquid Waste Incinerator.

Solid Waste Incinerator

It is similar as above shown only difference we require one pyrolizer or Rotary kiln before incinerator combustion chamber. In rotary kiln we charge solid waste through a conveyor, this kiln rotates at very low RPM between 0.5 to 1 rotation per minute. The temperature of kiln or pyrolizer is maintained around 800 to 850 ⁰C by burning fuel through fuel burners. All the organic material present in solid waste burn and remaining non-combustible solid discharge from other end of the kiln. Hot flue gases enter into next combustion chamber where temperature is further increased around 1100 to 1150 ⁰C to incinerate chloride impurities. Subsequently follow the similar path as described in Liquid Waste incinerator.

The solid waste which non-incinerable is send for secured land fill sites, however this not a suitable method of waste disposable. Below is the photo of a solid waste incinerator installation.

Dioxins are not usually present in waste, but they can form when chlorine-containing organic substances are burned. Modern incinerators produce dioxins and furans from three points in the process: stack-gas emissions, bottom ash, and fly ash. Operating Incinerator at higher temperatures above 1100°C is considered the most effective way to destroy dioxins.

Presence of Dioxins in our environment can cause cancer, reproductive and developmental problems, damage to the immune system, and can interfere with hormones.

Spray Dryer for Inorganic Aqueous Waste

In case when inorganic salts are presents in aqueous waste such as NaCl, MgCl2, Na2SO4, we can use spray dryer chamber. In this case we do not produce waste steam and here we use a spray chamber in place of the waste heat boiler. Rest other equipment remain as it is as liquid waste incinerator. Here hot flue gases at 800 to 850 ⁰C coming out from the combustion chamber enters into the spray dryer. Aqueous inorganic waste is sprayed through a nozzle from top, water gets evaporated and comes out with flue gases while dry solid salt is collected from the bottom of spray dryer. Which can be reused or sold depending on the quality otherwise goes for secured land fill sites.

ETP for Waste Water Treatment

We use Effluent treatment plants (ETP) for the removal of high amounts of biodegradable organic compounds, tar, debris, dirt, toxic, non-toxic materials and polymers etc. from the industrial waste water. The typical process steps for a ETP are as below:

• First remove any oil or tar from liquid surface through grease trap,
• Addition of flocculant to enrich organic matter in wastewater,
• Filtration and collection of solids (solid waste)
• Destroy large organic molecules in wastewater using oxidation methods,
• Adjust PH 7-8 with sodium hydroxide and flow into anaerobic process,
• Effluent passes through aerobic tank, converting all organic molecules into carbon dioxide, water and biomass (sludge) which we can be remove from the effluent.

Subsequently mass flows into a sedimentation tank and air flotation machine to remove biomass/sludge.

The waste water which contains non-biodegradable chemicals such as insecticides, pesticides, synthetic fibers, pyridines, cyanopyridines, ammonical impurities, glass objects, mercury, lead, arsenic etc., we use incineration method for treatment.

Conclusion

Effluent treatment technology is a continuously evolving field and require new ecofriendly and energy efficient ways. Because treatment of effluent is a cost and it reduces profit margin. Simultaneously, engineers should keep on working to reduce the effluent generation inside the plant using new technologies. Also, we need to look into the recycling of the effluent so that final effluent quantity is minimum for treatment requirement.

Thanks for reading…

The post Effluent Generation & Its Treatment Methods appeared first on ChemEnggHelp.

There are many advantages in using a liquid jet pump for certain applications, where fluid viscosity is low, fluid is not highly volatile, not very erosive in nature, has no sticky or polymerizing tendency, etc. The benefits of liquid jet pump use in such applications can be like, no moving parts, in line mixing, no or low maintenance and comparatively simple system.  

Principle of Liquid Jet Pump

In operation a high velocity jet of pressurised liquid discharged from the motive nozzle produces a region of low pressure in the suction chamber that entrains the secondary liquid or fluidised solid. The two streams then thoroughly mix in the throat before the resulting mixture flows through the diverging cone to regain some pressure to overcome system discharge heads.

Liquid jet pumps, utilize the pressure energy of a high-pressure fluid stream to boost the pressure and/or flow of a low-pressure fluid stream.

Ejectors are generally inefficient devices. However, their simplicity and lack of moving parts make them worthy of consideration, particularly where a high-pressure fluid stream is already available. This way we can use the available waste energy and can save energy cost for the process.

Performance of the Liquid Jet Pump

Let us refer the below simple liquid-liquid jet pump sketch.

Let us assume at Section-1, two fluids are mixing Stream-1 having mass flow rate W1 (kg/s) and Stream-2 with mass flow rate W2 (kg/s). The flow area for Stream-1, for Stream-2 is S2 (m2) and at Section-2 flow area is S3 (m2).

Mass Balance for the System

Here we can write the mass balance at steady state between Section-1 and Section-2,

W1 + W2 = W3                (here W3 (kg/s) is the mass flow rate at Section-2)

ρ1*V1*S1 + ρ2*V2*S2 = ρ3*V3*S3         -Eq.1     (i.e., rate of mass in at Section-1 = rate of mass out at Section-2)

since this is a liquid and can be assumed as an incompressible fluid hence, ρ1= ρ2= ρ3= ρ

Also, from geometry we can have, S1 + S2 = S3                 -Eq-2

Therefore, we can rewrite above Eq.1 with the help of Eq.2 and above assumptions:

V1*S1 + V2*S2 = V3*(S1 + S2)

(S2/S1) = [(V1 -V3)/(V3 – V2)]              -Eq.3

Momentum Balance for the System

Assuming negligible friction, the momentum balance can be written as below:

Rate of momentum in – Rate of momentum out = 0         (for steady state flow)

W1*V1 + W2*V2 – W3*V3 + P1*S1 + P2*S2 – P3*S3 = 0              

We can solve the above equation for discharge pressure,

P3 = (W1*V1 + W2*V2 – W3*V3 + P1*S1 + P2*S2)/S3                   -Eq.4

Hence, using above equations we can estimate the inlet pressure and flow rates to meet the required discharge flow rate and pressure requirements.

Various Applications of Liquid Jet Pump

We can find various industrial application of Liquid Jet Pumps as below:

• Eductors Inside as Storage Tank for mixing the liquid inside. In many cases such as dilution of incoming feed into the tank or when there are multiple streams are coming into the tank with different composition. In such cases Eductors can be very helpful and below figure shows the typical installation.

Here, the pump provides high pressure liquid stream which passes through the jet pump or eductor nozzle and pumps the tank liquid to make it a homogeneous mixture. This way we can avoid the installation of large size agitators and motor power consumption.

• Second application we can see for inline dilution of some concentrated solution. Many times, we use dilute NaOH solution for our process requirements and available is of 48% concentration. So, in such cases we can use an inline liquid-liquid ejector to get the desired dilute caustic solution. The typical installation in such cases can be as shown in below figure.

So, this way we can avoid a mixing vessel and can get continuous feed of dilute caustic solution.

• Another use we can see to pump the liquid using available high-pressure liquid. This way we can use available waste energy and can save power bill for the process. This type of arrangement we can understand by below figure.

As we can see in above figure, the primary fluid is passed through a nozzle where the pressure energy is converted into kinetic energy. The high-velocity jet entrains the secondary fluid. The two streams mix in the mixing tube, leading to pressure recovery. Further static pressure is recovered in a narrow-angle diffuser downstream of the mixing tube.

• High pressure liquid jet generates a vacuum, which we can use to diffuse the gas into the mixing chamber. As the gas/liquid mixture enters the diffuser, the static pressure begins to recover. This way gas is compressed as it approaches into the discharge. This way, we can see the Liquid Ejector works as an evacuator as well as a compressor also.

Conclusion

Liquid Jet Pumps/Ejectors are available in stainless steel, carbon steel, duplex steel, Hastelloy, titanium, rubber lined, PP, PTFE and PVDF. Liquid jet ejectors are jet pumps, which uses high pressure liquid as motive fluid. They use the kinetic energy of the pressurized liquid to entrain liquid, gases or vapours. Moreover, these can be used for pumping slurries and other liquids or granular solids. These devices discharge the resultant mixture against a higher pressure.

We should look into the plant and should find the applications of liquid jet pumps. As this will save the power bill required for pumping or generating vacuum. Also, this is the idea of creating wealth from waste energy, where we have high pressure liquid stream available.

Thanks for reading..

The post <strong>Liquid Jet Pumps</strong> appeared first on ChemEnggHelp.

Impact of Heat Exchanger Fouling

In chemical plants heat exchanger fouling is a big problem and this causes loss of revenue in terms of equipment replacement cost, maintenance & cleaning expanses. Moreover, fouling is responsible for productivity loss also as fouling of heat exchanger force us to continuously keep on reducing the raw material or input feed rates to the plant. In a shell & tube type heat exchanger fouling can be inside and outside surface of the tubes. Due to increase in fouling thickness, heat transfer resistance increases which continuously bring down the operating heat duty of the heat exchanger. And, finally when this operating heat duty is too low to operate the plant above its minimum turndown capacity, we need to shut down the plant to clean the heat exchanger.

Below is the figure showing shell & tube heat exchanger fouling at outside surface of the tubes:

To understand the heat exchanger fouling at inside surface of the tubes please refer to the below figure:

Most of the time we can clean the fouled surface and restart the plant for normal operation. But, is some cases where this fouling is impossible to remove, we need to replace the fouled heat exchanger with new equipment.

In a heat exchanger, deposition of fouling reduces overall heat transfer coefficient. Because of this heat transfer efficiency of the equipment reduces. According to a study, roughly build-up of a 0.6mm thick layer of fouling & scaling in tubes can reduce chiller efficiency by 20% approximately.

Causes of fouling in Heat Exchangers

We can classify various causes of fouling in heat exchangers in below three broad categories: –

Slurry & tarry material in fluid

There are fluids containing slurry or tar which we handle in our plants. This will settle & deposit on tube surface at low fluid velocity. This is generally a soft scaling or fouling and can be cleaned easily using low pressure water jets. The example of this is reaction product liquid containing catalyst fine particles or slurry of a crystallized material.

Dissolved Solid or Salts

In other cases, we can see some fluid containing dissolved solids like sodium chloride & water. When this fluid is heated in a heat exchanger (i.e., vaporizer) because of boiling at tube surface water evaporates but dissolved salt is non-volatile and remains on tube surface. In due course of time this deposition keeps on building and causes hard fouling of salts. To clean this, we need high pressure jets and wire brush. This fouling we can see in distillation column condensers (i.e., primarily operating at high condensing vapor temperatures around > 120 ⁰C), where we use cooling water as cooling utility. At this temperature dissolved solids present in cooling water retain at inside tube surface because localized boiling phenomena. This fouling we can see mostly at the vapour inlet side of the exchanger.

Miscellaneous Reasons

Many fluids have tendency to polymerize or form tar at high temperature. When we heat or boil this type of fluid using reboilers in distillation column bottom, after a certain operating cycle tubes of reboiler chock and cleaning is required.  

Overcooling of a fluid below its freezing point over a heat transfer surface causes coating of frozen fluid layer. This we type of fouling we know as a freezing fouling.

Other cause of fouling can be wrong selection of metallurgy, in such case due to corrosion metal surface get corroded and creates fouling on heat transfer surface.

Dealing with the Heat Exchanger Fouling

As we discussed above, fouling is heat exchanger is a serious problem for an efficient plant operation. Hence, as a process engineer, we need design the heat exchanger to deliver efficient working time span. So that, this can tackle fouling problem effectively. Below are some practical solutions, which we can consider:

Considerations during Design

One strategy we can opt, during heat exchanger designing is, keeping more fouling fluid inside the tubes. While, less fouling fluid we should keep in shell side. This type of arrangement facilitates us to easy cleaning of tubes from inside using water jet or wire brush to remove deposited fouling. As it is very difficult to clean the shell side fouling comparatively.

However, shell side cleaning, which is the removal of scaling or fouling from outside surface of the tubes. We can use suitable chemicals circulation methods through shell side, which can dissolve of remove deposited scale on the tubes outer surface. Chemical removal of fouling in heat exchanger we can achieve, in some cases by weak acid, special solvents, and so on.

Where, shell side fouling is too much, there we can select U-Tube bundle and shell type arrangement instead of fixed tube sheet type exchanger. After fouling we can open the heat exchanger and pull out the tube bundle to do the cleaning.

Considerations During Operation

Avoid large temperature gradients for heating with steam and thermic fluid. We should keep temperature gradients for heating around 30-35 ⁰C in case of organics and 35-40 ⁰C for the aqueous solution. This will minimize hard scaling on the process side due to over heating of the chemical on the tube surface. Also, we should use saturated steam into the reboilers.

In condensers and coolers tube side velocity (i.e., cooling water side) should be sufficiently high (around 6 – 8 ft/s minimum) to ensure the self-cleaning of the tube surface.

For viscous, sticky & slurry type materials we can use scrap surface heat exchangers. For example, a super saturated fluid is likely to crystallise on cooling & degree of fouling is very high. We can use scraped-surface heat exchangers in which a rotating element has spring-loaded scraper blades which wipe the surface of the tubes for efficient heat transfer.

Where fouling is the part of the process and unavoidable, we can consider a standby equipment in line. So, when one gets fouled take other in line and clean the fouled heat exchanger for next cycle. This way we can achieve uninterrupted plant operation.

Selection of compatible metallurgy will avoid the corrosion fouling of the heat exchanger tubes. We should provide temperature interlocks and controls to eliminate the possibility of freezing fouling, wherever we are dealing with possible below freezing temperatures.  

Cooling Tower Parameters Monitoring

In case of condensers & coolers, where we use cooling water, there we need to monitor and maintain the cooling tower parameters (i.e., TDS & pH) regularly. Cooling tower blowdown, side stream filter and chemical dozing are the measures to control the cooling water quality. These measures help us to control the total dissolved solid, suspended solids, microbiofoulants such as slime and algae and macrobiofoulants such as snails and barnacles in circulation cooling water.

Fouling in tubeside because of untreated cooling water and no side stream filter provision in Cooling Tower.https://www.chemengghelp.com/wp-content/uploads/2026/03/FouledHE.mp4

Conclusion

Finally, we understand that fouling in heat exchanger is the inherent part of the chemical process operation in heat transfer surfaces, especially in heat exchangers. Therefore, as a process engineer and plant operator it is very important to understand the causes and nature of possible fouling. This understanding will enable us to handle the fouling deposition effectively and we can keep our plant running for a longer span of time. In many cases we can avoid the damage of costly equipment altogether.

I assume this article will help you to understand & effective dealing with fouling of heat transfer surfaces.

Thanks for reading..

The post Fouling in Heat Exchangers appeared first on ChemEnggHelp.

Why Data is Important to Us?

• For the successful organizations data is a common language for all the communications. When we talk based on data, the chances of ambiguity and confusion is minimum and all are on same communication platform.  
• This common language makes our objective clear and facilitate the fast & corrects decision making.
• In a process data tells us where is the problem and how big that problem is? Moreover, using data we can identify where are we right now and easily quantify where we want to be in future? In other words, we can say it is data which tells us the problem and after solution it is data only which answers about the implemented solution efficacy.
• In Lean Six Sigma or DMAIC methodology data is the basis and good data collection simplifies the problem-solving efforts.
• Data is like a blood for any process or machine and variation in these data tells us about the performance & health of that process or machine.

 So, how many types of data we come across, let us understand in next section.

Types of Data

Broadly, we can divide data in two types as explained below:

Discrete Data

This type of data can take limited number of values like pass/fail, ok/not ok, true/false, win/loss, etc. A discrete process output describes an event. In plant operation we can find these data in the example of a batch reactor output result and can represent in a table as below:

Discrete data provides us the qualitative analysis for the process. Other examples can be processing for NOC application for a new plant – outcome can be either ‘Accepted’ or ‘Rejected’. One more employee satisfaction survey by HR people – results of this is either ‘Yes’ or ‘No’.

Also, we can collect categorical data in orderly form such as, ‘High’, ‘Medium’, ‘Low’. Other form of data collection can be categorical, like data collection for various types of industries in share market – ‘Chemical’, ‘Pharma’, ’FMGC’, ‘Oil & Gas’, ‘Automobile’, ‘Finance & Banking’, etc.

Continuous Data

These are the data for which we require an instrument to measure. We can express these data in either fractions or whole numbers. Like we need a temperature gauge or thermocouple to measure temperature, for pressure we need pressure transmitter or a gauge, flow rate measurement data can be collected using rotameter or an orifice meter.

We can represent these data in form of table and graph, for example steam feed rate in distillation column reboiler:

To understand continuous data characteristics, we need to estimate below parameters:

• Central Tendency of the Data – This we can estimate by calculating mean, median & mode for the given data set. If mean, median is same then we can say our data is uniformly distributed around the mean and symmetrical. In other case when mean ≠ median, then our data will be skewed in shape.
• Dispersion of the Data – To check this we have two parameters first is range and second standard deviation. Higher values of range and standard deviation shows that our data is more dispersed and variation in process is huge. On other side data with lower range and standard deviation values tells our process or machine is running more stable.

Calculation of Mean, Median & Mode

For a given data set we can estimate mean, median & mode to check the central tendency & shape. Below are the relationships to estimate these parameters:

Mean – In a given data set mean is the arithmetic average of all the data points.

Where n = number of data points

Median – After arranging a data set in the ascending or descending order, the middle data point of the data set is Median. When we have even data points then it will be the average of two middle data points.

Mode – This is a parameter in a data set which tell us about the most frequently occurring data point. For example, if we collect the data for various items sold in a day from a super, the mode of this data set will tell us which item has most demand.

Measuring of Data Spread or Dispersion

To estimate the data dispersion, we can use below parameters:

Range – When we see a data set in this there will be a data point having minimum value and one point will have maximum value. So, the difference between this maximum & minimum data point is Range for that data set. Higher range means process in less stable and has poor control.

Variance / Standard Deviation – Other parameter which measure how each data points are spread around the mean.

If standard deviation is lower, spread of data will be also lower around the mean and performance of that process in more stable & predictable.

Understanding the Shape of Data Distribution

Based on data points spread around the mean we can classify shape of data distribution in two types as below:

Symmetric Data Set – In this type spread of data points in a given data set is identical around the mean. And, for such data sets mean, median & mode are same.

Asymmetric Data Sets – In this type of data sets distribution of data points around the mean is not equal. The distribution will be skewed at either side of the mean as shown in above figure. In case of positive skew mean is lower than the mean and data spread will be high on the right side of the mean. While for negative or left skew, there is high spread of the data points on the left side of the mean.

Performance Baselining Using Data

To start any improvement initiative first we need to collect the data for that parameter of interest or CTQ (Critical to Quality). For example, we can be interested in reactor yield maximizing, distillation column steam norm reduction, batch cycle time minimization, etc. So, for all these cases we need to collect the data for these parameters to see the present performance level. These data will provide us a reference point from where we will measure the process improvement performance. This reference point we call the ‘Baseline’.

For many cases where historical data is not available for our CTQ, in that situation to access the present level performance there we collect data by sampling. Subsequently we calculate the baseline for our improvement project. Let us take an example for reactor yield as below to estimate the baseline:

So, from descriptive statics of the reactor yield data set we can find following observations:

Mean is 82.11% and median is 81.98% which are very close to each other. Hence, we can say this process is behaving normally and we can consider Mean (i.e., 82.11%) as a project baseline. This we can confirm by P-value also which is >0.05 for normality pass test.

Conclusion

Finally, we discussed about the need of data, why data is important for us? Then we discussed about the type of data and their characteristics. Also, learned how to estimate various parameters to understand the data set shape and spread of data points. As data is the language of the process therefore, we need to understand the data properly.

At its core data is about making predictions about the process. Using real time data generating from the process, we can develop machine learning algorithms, which can be used to derive AI or artificial intelligence. This artificial intelligence we can use to make timely smart decisions, which in result will provide strategic advantages to the business in terms of higher market shares and better profit margin. Moreover, we can use data with artificial intelligence to make our plant operation safer and more environmentally friendly.

I guess now you can understand how valuable is the data. Using data analytics tools we can get valuable insight about the process. Thanks for reading.

The post Understanding of Data appeared first on ChemEnggHelp.

What is Six Sigma?

When we talk about six sigma, it means our process efficiency is 99.99966%. In other words, we can say there will be only 3.4 defects generation per 1000000 opportunities. Therefore, our process sigma level is directly related with product quality and product cost. Below matrix gives us a clear picture sigma level and cost of quality for our product manufacturing.

So, you can see it is evident being better is cheaper for any company. Now we will dive into step-by-step process to understand the DMAIC methodology. DMAIC is the short form of Define, Measure, Analyse, Improve and Control phases. First, let us talk about Define phase.

Define Phase

Define is the first and very important phase for any improvement project. This is the foundation of any successful project. You should understand a project will be successful or fail mostly depends on this phase.

The objective of this step is to recognise and understand the need of our stakeholders. Whether this project is important or not for them. Your stakeholders can be external or internal. External stakeholders are such as suppliers, customers, local administration, pollution control body, society, shareholders, etc. When we talk about internal stakeholders, it means those who are directly concerned with your project. They can be like, your manager, business head, plant manager, site head, etc.

Various activities in this phase are as below:

Identification of Project CTQ’s

CTQ is the abbreviation for Critical to Quality. For a project this is a characteristic of a product or a service that satisfies a customer requirement or process requirement. In a project there can be more than one CTQs. You can think various examples for CTQs in a business such as cost of product, numbers of customer complaints, employee attrition rate, % sales growth per year, etc.

Therefore, we can see the CTQ is the VOC (voice of customer) or VOB (voice of business), which is the pain area or need of a customer or a business. Let’s understand the CTQ identification exercise with an example VOC for Product Variable Cost reduction by 10%, which the need of your customer.

CTQ Identification for Product VC Reduction

Here we have taken a hypothetical product case, in which we are using two raw materials Chemical A & B. Other than this we are using Steam and Power as utilities. Moreover, other overhead cost includes like packaging cost, logistics cost and employee cost. This we can see in below figure.

In above exercise we can see there are total 7 nos of CTQs, which leads to the customers need through drivers. Therefore, if we address these CTQs then our customer or stakeholder will be satisfied.

Project ‘Y’

Now, these 7 CTQs will lead us to Project ‘Y’. This is the actual project on which we will work to improve the project CTQs. In our example these are as in below table:

So here we got seven projects, in reality it is not possible to take up all the projects simultaneously. Because every project needs resources which are limited such as man, machine and money. Therefore, it is necessary to prioritise your projects. It means you must take up high impact projects first and subsequently you can work upon other projects as well.

To prioritize the projects, we can use Pareto analysis of Prioritization Matrix. Here we will use Pareto Analysis, it says our 80% of benefits comes from 20% of work. We will make Pareto chart for our all CTQs based on their contribution in the product variable cost.

Pareto Chart

This is a statistical tool developed by Vifredo Pareto in 1896 and used for decision making. This is also known as 80:20 rule also. In our example contribution of various CTQs are in below table.

You can prepare Pareto chart in excel first put the contribution cost in descending order. And, add one more column showing cumulative contribution.

From above you can see if you focus on first 2 CTQs, that will address over 70% total variable cost of the product. Therefore, working on these two CTQs related projects will lead you towards major impact on product cost reduction.

Project Baselining

After freezing the CTQs and the Project ‘Ys’, you should collect the data for Project ‘Y’. In our case this is consumption norm of chemical ‘A’ and ‘B’. It is better we collect data for one year of consistent plant operation. Because in a year you can see the impact of seasonal change also. After collection of one year of data for the norms, just draw a Run Chart. This chart will give us the behaviour of our process over the year. In case there are any shutdown or breakdown we can see it in run chart. Remove these data points and estimate the mean as a baseline for your project.

When data are not normal then we should consider median as the baseline of our project. Because in that case mean will not give us a realistic representation of the operating process.

SIPOC (Supplier Input Process Output Customer)

In Lean Six Sigma we use SIPOC to identify the relationship between response (outputs) and independent variables (inputs) or in other words Y = f(X). Here, we try to recognize the suppliers which provides inputs to the process and customers who uses outputs from the process. You need to prepare a SIPOC for your project in the define phase of the six sigma project.

Let us consider the example for reducing steam consumption norm for a distillation column. For this below can be a typical SIPOC Diagram:

Benefits of SIPOC are mainly two, first it gives us understanding of the process from highest level. And, second it helps us to draw the scope of the project.

Project Charter

We need to understand this clearly that any Six Sigma project is a team work. Basis of six sigma is to develop cultural change in the organization for continuous improvement with sustenance. A Project Charter is a written document and which is an agreement between management and project team, about the project scope of work and goal. This project can be a new plant project, existing plant de-bottlenecking, process improvement initiative, plant maintenance work, new product development or plant digital transformation campaign, etc.

Below is the typical format of a project charter and this a very important deliverable of Define phase of six sigma project. It is very important to get signoff this project charter from all the stake holders named in this document.

Stakeholder Analysis

Whoever is affected directly or indirectly by the business operation are considered its stakeholders. These can be like, suppliers, customers, company management, its employees, families of employees, people living in vicinity, government, financers, shareholders, etc.

The stakeholder support is very critical for the success of any business. During the project cycle we need support from many stakeholders at various levels. So, it is necessary for you to carryout stakeholder analysis to understand and evaluate their support requirement. Subsequently you need to prepare a strategy to getting their support for the overall success of the project. When we talk about overall success it means working with man & machine both at the same time.

For this purpose, you can use RACI Matrix, which stands for Responsible, Accountable, Consulted & Informed. Example of RACI Matrix for a Six Sigma project can be as below:

In a Six Sigma project we need a cross functional team as we may need different functional inputs to solve the problem. A Six Sigma team is formed to include respective domain knowledge experts, as we need this expertise to find out the solution. For example, if we are looking to reduce steam consumption norm in distillation column, we need to include a Chemical Engineer (from Process Design Department). Similarly for procurement lead time reduction we require purchase manager in our team. For recruitment time reduction project, we need Human Resource Manager as a team member.

Communication Strategy

A proper communication plan is very important for the overall success of the project and it is must to prepare a communication strategy in define phase of six sigma project itself. This will eliminate the confusions & surprises during project. A good communication plan includes following things:

• Who will communicate?
• What to communicate?
• When & at what frequency communication will be done?
• It is important to mention the reason of communication.
• Who will be the recipient of the communication and what will be the mode of communication? Like written, verbal or meeting.

Conclusion

So, end of the define phase we should have performed following things typically:

• We have conducted first meeting with the project team and discussed about the goal of the project. Team members and their roles are clear with timebound deliverables.
• High level project schedule is ready with measure Milestones.
• Cost benefit analysis of the project is completed.
• Data collection is completed for the project CTQ with Run chart preparation. Project baseline is frozen.
• Project charter is ready and signed off with all the stakeholders.
• Stakeholder analysis is done and a communication plant is ready with us.

Once Define phase is completed, we are ready to move towards the next phase of our Six Sigma project which Measure phase.

Thanks for reading…

The post Six Sigma Methodology – Define Phase appeared first on ChemEnggHelp.

So, let us understand the fundamentals behind a VAHP working as below.

What is Vapour Absorption Refrigeration Cycle?

As we discussed above VAHP works upon vapour absorption refrigeration cycle. In this process there are two working fluids – one is refrigerant and other is absorbent. So, to generate chilled water @ 7.0 ⁰C we use LiBr (lithium bromide) as an absorbent and water as refrigerant. And, to generate chilled brine, we use ammonia and water working fluids. Where, ammonia is refrigerant and water is absorbent.

The below are two important properties which are the basis for working a VAHP (with LiBr and water working fluids):

• Boiling point of water is the function of pressure, as we reduce the pressure its boiling point reduces. So, we can see at 6 mmHg absolute pressure water boils at 3.7 ⁰C.
• Second important property is the Lithium Bromide affinity towards water. So, this concentrated LiBr aqueous solution can absorb water vapours.  

Now, we will see how above two properties works in absorption refrigeration cycle. You can refer the below figure to understand this principle.

Various Part of a VAHP and their Function

A vapour absorption heat pump or VAHP has different sections as we can see in above figure. There is evaporator, absorber, regenerator, condenser, circulation pumps and vacuum pump. The utility of each part we can understand as given below:

Evaporator

In evaporator we maintain vacuum around at 6 mmHg absolute and chilled water provide the heat to this water (refrigerant) for evaporation at 3.7 ⁰C. After supplying heat chilled water cool down to around 7.0 ⁰C. The chilled water inlet temperature to evaporator is around 13.0 ⁰C. These vapour at 3.7 ⁰C from evaporator goes into the absorber section.

Absorber

Where concentrated solution of LiBr (absorbent) absorbs this water vapour. This concentrated solution of absorbent we get from regenerator. And the lean solution of absorbent from absorber goes back into the regeneration section. For circulation of this absorbent, we use absorbent circulation pump.

Regenerator

In regenerator we regenerate lean LiBr solution, by evaporating excess water. For this purpose, we use waste heat, which is a low-pressure steam @ 2.0 kg/cm²g. Here, water evaporates and vapour goes into a condenser, while concentrated absorbent solution goes into the absorber. Other than steam many VAHP operates at hot water also, in that case this regenerator will operates under vacuum. This way we can evaporate water from the lean LiBr solution at low temperatures also. Moreover, VAHP can be double effect type, where we need steam supply at higher pressures. For your clarification the above figure is for a single effect VAHP, having LiBr and water as a working fluid.

Condenser

So, we need a condenser which is a shell & tube type heat exchanger to condense the water vapour generating from regenerator. Here this water is our refrigerant and we use cooling water to condense it. After condensation this refrigerant goes into the evaporator again, which is operating at vacuum of 6 mmHg absolute. This way this refrigeration cycle keeps on working.

We can find the fundamental difference between a vapour compression and vapour absorption is a compressor. In compression refrigeration cycle we use a compressor to compress the refrigerant vapour. While in absorption cycle, we use absorbent to condense/absorb the vapours.

In summary, we supply heat to regenerator using steam and remove heat in evaporator from circulating chilled water. And, remove heat from condenser using cooling water. This way our VAHP generates chilled water at around 7.0 ⁰C temperature. This chilled water temperature depends on the evaporator section vacuum, if vacuum reduces chilled water supply temperature will increase. Simultaneously, condenser cooling water supply temperature is also important. Because condensed refrigerant (i.e., water) temperature will depend on cooling water temperature.

Types of Vapour Absorption Heat Pump

In our industries we can find two types of VAHP first is single effect which require low pressure steam (i.e., around 2.0 kg/cm²g). While second type is double effect VAHP, which operates at higher pressure around 5.0 – 8.0 kg/cm²g steam supply pressure.

In double effect VAHP there are two generators while in single effect we have one generator. So, water vapour generating from first regenerator goes into the second regenerator. This way we can achieve low steam consumption to evaporate the same amount of water from lean LiBr solution.

So, benefit of two effect VAHP over single effect is the specific steam consumption to generate same TR. The specific steam consumption in single effect VAHP is 7.5 – 8.0 kg/TR, while for double effect this as low as 4.5 – 5.0 kg/TR. Therefore, double effect VAHP gives advantage of around 35 – 40% lower steam consumption.  

Coefficient of Performance (COP) of a VAHP

We can measure the performance of a refrigeration machine by estimating it’s COP or coefficient of performance. The COP for a VAHP we can estimate using below relationship:

If we designate the Q₁ = Heat supplied by steam in regenerator or heat added from source at T₁ and Q₃ = Heat supplied by chilled water in evaporator or heat absorbed for refrigeration at T₃. And, T₂ is the ambient temperature. Then, we can rewrite above relationship as below:

So, if our VAHP is operating at 2.0 kg/cm²g and has regenerator temperature 100 ⁰C (373 K) and evaporator temperature is 4 ⁰C (277 K). Considering ambient temperature 35 ⁰C (308 K), COP will be = [277*(373 – 308)]/[373*(308 – 277)] = 1.56.

Cost Benefit Analysis Vapour Absorption v/s Vapour Refrigeration System

Ideally a VAHP is advantageous when we have waste heat available in our plants. When we talk about waste heat is means, we are rejecting this heat into our cooling towers or atmosphere. Moreover, there are conditions where power cost is very high in comparison with steam cost, then use of VAHP is a cost-effective option.

So, to understand the economic feasibility let’s consider a plant where we require 100 TR refrigeration in terms of chilled water. We have option to go for a vapour compressor refrigeration unit or a single effect VAHP. Below table is the working to understand this comparison which can help us to take better decision.

We have made following assumptions for our estimation:

• Power consumption in refrigeration compression system 0.7 kWh/TR
• Steam consumption is VAHP 5.0 kg/TR
• Power cost @ 6.5 Rs/kWh and steam cost @ 0.5 Rs/kg
• Plant operating hours = 8000 hrs/annum
• All other overhead cost is same in both cases

Therefore, from above analysis we can see, by selecting VAHP over refrigeration compressor is preferable. As, there will be annual savings in operating cost around Rs.16.40 lacs. However, investment requirement for VAHP is higher by Rs.10 Lacs (35 -25 = 10). The simple pay back period for the differential investment will be =10*12/16.4 = 7.3 months. 

Conclusion

Finally, in this article we discussed about vapour absorption refrigeration system based on LiBr-Water working fluids. This can provide refrigeration requirement up to 7.0 ⁰C. For refrigeration requirements at lower temperature say (-) 18 ⁰C, we use NH3-Water as working fluids. This VAHP operates under pressure to condense the ammonia vapours coming out from regenerator. Subsequently, liquid ammonia is throttled into the evaporator to generate chilled brine utility. From evaporator ammonia gas goes into the absorber, where water is used to absorb the ammonia gas.

So, we should explore the avenues of waste heat available in our plants. Various possible sources can be such as reactor outlet hot gases or heat of reaction, condensate flash steam, hot process streams, hot flue gases, etc. This waste heat we can use to generate low pressure steam or hot water and can use in VAHP refrigeration system. These VAHP refrigeration machines will help us to stop our refrigeration compressor, which are one the major power consumers in our plants. This way we can reduce the overall power consumption, which is ultimately a reduction in variable cost of the product.

Moreover, using VAHP is good for our environment sustenance, where we are not using any harmful refrigerants. Simultaneously, it encourages the use of waste heat available inside the plants to generate low-cost refrigeration. Consequently, which is the effort towards reduce carbon foot prints.

Thanks for reading and looking forward for your comments!!!

The post Vapour Absorption Refrigeration Cycle in VAHP appeared first on ChemEnggHelp.

In fermenters we mix molasses and water with pre-activated yeast. Here, biological reaction in the absence of oxygen takes place and glucose is converted into ethanol and CO2. This we also know by the name of fermentation process. At the end of fermentation process, fermenter contains ethanol in the range between 6 to 11 % by volume.

This reaction mass after completion of fermentation process is known by fermented wash. The ethanol concentration in fermented wash depends on the fermentation technology which we are using.

For traditional batch fermentation process ethanol concentration is low in fermented wash, around 7-9% by volume. While in Fed Batch process, which is a semi-batch process it is around 9-11% by volume.

In this article we will discuss the ethanol distillation process from fermented wash. Moreover, we will do energy balance and subsequently discuss the energy saving opportunities also. This is very important to make your alcohol business more cost competitive and sustainable.

Process Flow Diagram for Distillation Section

To understand the ethanol distillation process in a distillery you can refer the below figure. This set up is to produce Rectified Sprit or RS. Here you can see, we have two distillation columns in series. The fermented wash from fermenter is pumped into the analyser column.

Analyser Column

In analyzer column we feed fermented wash contains 7-11 % ethanol contents by volume at top tray. While, live steam enter at bottom of the column. This is also a steam stripper column, which we use to strip off all the ethanol entering with feed. The top of analyzer column contains ethanol and water and this feed into the rectifier column. Bottom of the analyzer column has negligible ethanol and is an effluent stream. This effluent stream is known as spent wash in distillery. The spent wash contains bio mass and other harmful chemicals, which are dangerous for the environmental sustenance. Therefore, proper treatment of the spent wash is inevitable to ensure zero liquid discharge from the distillery.

Rectifier Column

In rectifier column we recover rectified sprit from the top and bottom is a waste stream, contains negligible amount of alcohol. This effluent stream is known as spent lees. We recycle back spent lees for the molasses dilution process.  

Total liquid effluent generation from a distillery can be in the range of 7 – 10 kl/kl of ethanol production. This effluent generation norm depends on the fermentation technology which we are using.

Both the columns are tray type columns. This is so because the fermented wash contains bio-mass, salts and suspended solids. If we use packed column it will choke the column packing. Moreover, in analyser column we generally supply direct live steam for heat supply. The reason is same, as bottom stream of analyser column will choke the reboiler tubes.

Furthermore, we need to remove low boilers from rectified sprit, which forms during molasses fermentation. To do this we need to purge out small quantity frequently, from the top of the rectifier column. 

So, to understand the material and energy balance for RS distillation we will take an example. The basis for process calculation is in next section.

Operating Data for Distillery

For our study we will take an example of rectified sprit distillation or ethanol distillation setup in a distillery. The feed rate to the analyser column is 30000 kg/h and ethanol concentration in feed is 10 % (vol/vol). Analyser column feed inlet temperature is 80 ⁰C.

Material Balance and other properties of ethanol distillation is given in below table:

Heat balance for Analyzer Column

For estimating steam consumption for analyser column, you can follow below steps.

Feed rate to the analyser column is, F= 30000 kg/h, analyser column bottom temperature, T1= 110 ⁰C, Heat capacity of feed, Cp1= 1.0 kcal/kg⁰C, Latent heat of analyser column top vapor, LH1= 358 kcal/kg.

Since total alcohol in feed is 30000*8.13=2439 kg/h, and ethanol concentration in analyser column top is 55.56 wt%. So, analyser column top flow rate will be, M1= ((2439) – (30347*0.8/100)) *100/55.56 = 3953 kg/h

Therefore, heat load on analyser column will be, Q1= F*Cp1*(110 – 80) + 3953*LH1 = 30000*1.0*(110-80) + 3953*358 = 2,315,890 kcal/h

We will use 3.0 bar saturated steam for heating. So, latent heat of steam LH2= 517 kcal/kg and saturated temperature T1= 133.7 ⁰C.

Hence steam required for analyser column will be, W1= Q1/(LH2+Cp*(133.7-110)) = 2,315,890/(517+1.0*(133.7-110)= 4302  kg/h

For Analyzer Column calculate LP Steam feed rate will be, W1 = 4302 kg/h. Here we are feeding live steam into the column directly. However, it will be slightly higher side because of heat loss to surrounding and leakages from the piping and fittings. For this purpose, you can consider around 5% extra steam. Therefore, actual steam consumption for the analyser column will be around, W1’= 4302*1.05 = 4517 kg/h.

Heat Balance for Rectifier Column

So, to estimate the steam requirement for Rectifier Column. We need to know reflux ratio for the rectifier column. In our case we are considering Reflux Ratio of 1 : 4, hence vapour rate from the column will be,

M2 = (1 + 4) * 2292 = 11,460 kg/h            (here, 2292 kg/h is the distillate rate from rectifier)

Latent heat of vaporization for the rectified spirit is LH2 = 219 kcal/kg. Therefore, heat load for condenser will be Q_cond = 11,460 * 219 = 2,509,740 kcal/h.

Heat duty for rectifier column reboiler can be estimated by

Q_reb = Q_cond – heat supplied by the vapour feed

Latent heat of the vapour feed to the rectifier column is LH1 = 358 kcal/kg. Hence heat load on rectifier column reboiler will be

Q_reb = 2,509,740 – 3953 * 358 = 1,094,566 kcal/h

Steam & Cooling Water Requirements

Latent heat of 3 bar steam is LH2 = 517 kcal/kg. Hence steam requirement for the rectifier column will be

W2 = Q_reb /LH2 = 1,094,566/ 517 = 2117 kg/h

Hence total steam requirement will be W = W1 + W2 = 4302 + 2117 = 6419 kg/h, considering 5% heat loss from the system steam requirement will be W’ = 6419 * 1.05 = 6740 kg/h

If cooling water supply temperature is 32 ⁰C and temperature difference across the cooling water side is 6 ⁰C. We can estimate the cooling water requirement W3 = Q_cond/ (Cp * ∆T) = 2,509,740/(1.0*6) = 418,290 kg/h = 418,290/1000 = 418.3 m3/h.

Summary of Energy Balance

So, we can summarize the steam and cooling water requirements for both the columns as below:

RS (Rectifier Sprit) Production Capacity: 2292 kg/h or 55 TPD

Steam Consumption Norm: (6419/2292) = 2.80 kg/kg

Simulation Results for Distillery

In this section you can refer the ethanol distillation simulation results to cross check our above calculations. We will also see the design outputs for columns, reboiler and condenser.

From above simulation results you can see our material balance and heat balance calculation are OK.

Column Sizing Results

Now we will check the column sizing for this I am considering tray type columns. For analyser column we will consider 10mm diameter holes and 300mm tray spacing. And, for rectifier column we will take 5mm diameter holes and 300mm tray spacing.

Below are the results from simulation:

Energy Saving opportunities

So, from above calculations you can see steam consumption norm is 2.80 kg/kg. Therefore, if we take steam price @1.40 Rs/kg, then steam cost will be 2.80*1.40 = 3.92 Rs/kg. And for 50 TPD distillery capacity it will be 50000*3.92 = 196,000 Rs/day. For 280 days distillery operation this steam consumption bill will be 280*1.96 = 548.8 lacs. So, it is a huge money, if we target 10% reduction it will be 54.88 lacs.

Hence, various opportunities for energy savings can as below, which you can work out.

• Boiler water feed pre-heating using spent wash stream. In our case this is at 66 ⁰C and we can cool it down up to 45 ⁰C. So, total energy saving can be ES1= 30347*1.0*(66-45) = 637,287 kcal/h.
• Heat recovery from rectifier top is possible. Using this waste heat, we can preheat up to 67 ⁰C any plant stream or boiler feed water. We need to install an additional heat exchanger in series prior to condenser. If we consider recovery of latent heat only then, available heat opportunity will be ES2= 11460*219 = 2,509,740 kcal/h. This heat recovery will reduce cooling water requirement also. Which is ultimately saving of power consumption.
• Other opportunity we can consider is heat recovery from rectifier column bottom. Here, spent lees is available at 101 ⁰C and can be cooled down to 45 ⁰C. Therefore, available heat for feed preheating is ES3= 1649*1.0*(101-45) = 92,344 kcal/h.

This way if we sum up all the energy saving opportunities ES= ES1+ES2+ES3 = 3,239,371 kcal/h. And, if we convert this energy in 3 bar steam equivalents then, ES/517 = 6266 kg/h. However, major waste heat is available at low temperature levels (66 and 77 ⁰C), still we can use it for feed preheating. Other options for using this waste steam can be VAHP (vapor absorption heat pump), to generate chilled water. Also, we can use heat pump to convert this low temperature level waste heat into high temperature level valuable heat.

So, we can see the heat integration possibilities to extract these available waste heats. This will reduce our product cost and enhance business profitability.

Conclusion

Finally, we can say a thorough process analysis, material and energy balance for our ethanol distillation in distillery is very important. This gives us the insight of our process and enable to find out the possible opportunities for further improvements. I think you can use this article to maximize the energy efficiency of your distillery.

Thanks for your read and looking forward for the comments and feedbacks.

The post Ethanol Distillation (Rectified Sprit) in Distillery appeared first on ChemEnggHelp.

Extraction process works on the solute solubility difference between feed and solvent. Due to solubility difference mass transfer of solute takes place between phases. After extraction, we get solute rich phase, which is known as extract. And, other phase which has generally very low or negligible solute concentration is raffinate.    

As you know in chemical process industries, we use various kind of organic solvents like, benzene, ethyl-acetate, heptane, DMF, THF, toluene, methanol, etc. The selection of solvent for extraction depends on the particular process requirements.

Challenges in Organic Solvent Use

The use of these organic solvents poses challenges like handling and disposal issues. Apart from these, organic solvents create number of environmental concerns, such as atmospheric and land toxicity. Moreover, in many cases, conventional organic solvents are regulated as volatile organic compounds (VOCs). In addition, certain organic solvents are under restriction due to their ozone-layer-depletion potential.

So, to counter above challenges, super critical fluid solvent extraction can be a good alternative. Which you can explore further for your extraction process.

In this article we will discuss in details about the Super Critical Fluid (SFC) and Super Critical Fluid Extraction using CO2.

What is a Super Critical Fluid?

A substance beyond its critical point is known as the Super Critical Fluid (SCF) and in this state compound’s liquid-vapor phase boundary no longer exists. In other words, we can say that beyond critical point for a compound there is no distinction between liquid and vapor phase. To understand this phenomenon, you can refer the below figure.

Characteristics of Super Critical Fluid

 So, you can see in above T v/s P diagram, above critical point a substance is in super critical region. In this regime fluid properties undergo into remarkable changes and shows properties of liquid and gas both simultaneously. These properties we can list down as below.

1. Fluid has liquid like densities
2. Surface tension of fluid reduces, which is a liquid property
3. Viscosity of SCF is like gas
4. Diffusivities are higher than liquids
5. SCF has gas like compressibility

Therefore, in nutshell we can say Super Critical Fluid (SCF) is an excellent solvent for extraction process. As they have low surface tension and gas like diffusivities, which is good for higher mass transfer coefficients.

The solvent power of a super critical fluid is approximately proportional to its density. Thus, for SFC solvents we can change the solvent power by varying the temperature and pressure. As SFC solvents are strong function of temperature and pressure therefore, it is very convenient to adjust their properties. On the other side, for conventional organic solvents, you require relatively large pressure changes to change the density.

Various types of Common SCF Solvents

You can find many types of super critical fluid solvents which we use in chemical process industries. These are like CO2, Nitrous Oxide, Water, Ethane, Propylene, Propane, n-heptane, Ethanol, etc.

Below table shows you the critical properties of some SCF solvents.

In our chemical processes, we most widely use carbon di-oxide as SCF solvent for the extraction. The CO2 like Pentane and Hexane is very non-polar solvents; therefore, it is best solvent for oils and fats extraction. On other side water, nitrous oxide are polar solvents. And, Ethanol, Methanol and Acetone are in the middle of the polarity scale.

We can use mixture of SCF solvents to enhance the solubility of different solutes.

Why CO2 is the best SCF?

As I mentioned above in our chemical process industry CO2 is best SCF solvent, which we use in extraction process. The reason for this choice is many, which you can see are as follows:

1. It has lower critical pressure and temperature, which means comparatively lower operating cost for the extraction process among various other SCF solvents. Moreover, lower pressure and temperature will require lower thickness and pressure rating of equipment. In result, this will reduce overall capital cost of the plant setup.
2. Other excellent quality of CO2 is, its relatively non-toxicity and non-flammability. These both properties eliminate the possibilities of any hazardous related to process and people.
3. Apart form this CO2 is available at high purity and cost is also low. It is a non-reactive gas.
4. Separation of CO2 from extract phase is very easy. We need to just reduce the pressure and this will evaporate out from the mixture. The solubility of CO2 gas is also low or negligible in other chemicals.
5. It has polarity like liquid pentane at SCF conditions. Moreover, it is a good solvent for many nonpolar, and a few polar, low-molecular-weight compounds.

Important Parameters for a SCF Extraction Process Design

Now we will discuss about important parameters, which you should consider during the SCF Extraction Process design. We will go through them one by one as below:

• Threshold Pressure of SCF – This is the minimum required pressure at which a solute become soluble in SCF solvent. Generally, when we increase the pressure of a SCF solvent, the solubility of solute increases. But, after a particular pressure, solubility become constant. To understand it, you can refer to below typical diagram.

• Second parameter which is important for design point of view is the pressure at which a SCF solvent achieves maximum solubility. Knowing this pressure is important for deciding the pressure rating of equipment. Also, process design calculations will be based on this maximum solubility data.
• Apart from above, knowledge of the physical properties of the solute is very important. Based on solute characteristic various scenarios can be as below:
  1. There is no interaction between solute and solid phase, the process is dissolution of solute in suitable solvent.
  2. There can be interaction between solute and solid, in this case extraction is a desorption process. Here, adsorption isotherm of solute on the solid in presence of solvent determines the equilibrium conditions.
  3. The solid phase swell by the solvent. In that case extraction of entrapped solutes occurs through either dissolution or desorption mechanisms.
  4. In case is solute is reactive in nature, insoluble solutes react with solvent and products are soluble and we can extract it. The example of this is lignin extraction from cellulose.

Apart from above, other thermodynamic properties which are important for the SCF extraction system design are, temperature, pressure, equation of state, adsorption equilibrium constant, solute solubility, etc.

Process of SCF Solvent Extraction System

This SFC solvent extraction process can be in continuous or batch mode. In most of the cases it is in batch mode or we cab say semi-batch mode. Here, we charge feed in extractor vessel and keep on circulating SFC-CO2 through the extractor till complete solute is extracted from the feed.

To understand the typical process of SCF Solvent extraction system, you can refer below figure. In this process liquid CO2 enters into a compressor and discharge goes into the heater. Using compressor and heater liquid CO2 is converted into Super Critical Fluid (SCF). Subsequently we mix this SCF CO2 Solvent with feed inside an extractor. This extractor contains packing to provide surface are to enhance the mass transfer rate. In extractor solute transfer takes place from feed to SCF solvent at a particular temperature and pressure conditions.

From extractor, extract phase goes into a separator, while waste stream as raffinate we remove from the extractor. Inside separator vessel, pressure is reduced to a level where, solubility of solute is reduced. Consequently, solute separation takes place and CO2 in gaseous form goes into a condenser. Our product we collect from the bottom of the separator vessel.

The gaseous CO2 condenses into the condenser. And, liquid CO2 again recycle back into the liquid CO2 tank. This way this cycle keeps on continue and any loss of CO2 is fulfilled by a make CO2 gas.

Below are some special applications of SCF solvent extraction process for your reference.

• Extraction of vitamin E from natural resources
• Removal of fat from food
• Removal of pesticides
• Oleoresins extraction for red bell pepper
• Extraction of poisons
• Removal of alcohol from wine

Conclusion

Here we can see SCF solvent extraction has various advantages over conventional organic solvent extraction process. However, major disadvantage in SCF solvent extraction is, it requires high operating pressure. For instance, in case use of SCF-CO2 for Naphthalene extraction operating pressure range is 90 bar to 300 bar.

Therefore, this high pressure needs heavy thickness equipment and high-pressure rating piping, fittings & valves. Moreover, operating cost of the compressor is too high and economic feasibility of the process is under question.

Nevertheless, SCF-CO2 solvent extraction is best suitable for high value and temperature sensitive products. In addition, this provides non-toxic and non-flammable process, which very important in some processes.

Thanks for reading, looking forward for your comments!!!

The post Super Critical Fluid Solvent Extraction Process appeared first on ChemEnggHelp.

Process Details for Ammonia Recovery Column

You can refer to below figure to understand a typical ammonia recovery system. In this we have a distillation column which can be packed or tray type. This column operates at pressure around 5.0 bar, steam is supplied from reboiler and at top there is a partial condenser. Cooling water supply temperature is 32 ⁰C. And @ 5.0 bar column vapour temperature will be around 75 – 78 ⁰C. In partial condenser, partially condensed column vapour goes for reflux. And pure ammonia is recovered and recycle back in gas phase from this condenser. In this distillation column, reboiler can be natural thermosyphon or forced circulation type.

From above process flow diagram, you can understand the process of a typical ammonia recovery column. Aqueous ammonia feed from ammonia absorber enters into the ammonia recovery column via a feed preheater. In feed preheater we use waste heat of hot bottom outlet stream from ammonia recovery column to preheat the column feed. From reboiler heat is supplied to column; we use saturated steam in reboiler as a heating utility.

Column operates at 5.0 bar pressure and column top goes into a partial condenser. In partial condenser part of the vapor condense and goes as a reflux into the column. While ammonia gas recycle back to the process. In case of excess moisture carryover in recovered ammonia, you can provide a chiller. This chiller will condense the excess water content in recovered ammonia and recovered ammonia concentration will increase. The condensed water in form of ammonical solution goes back as reflux into the column.

Column bottom, which contains traces of ammonia and other impurities is sent for effluent treatment plant.

Material Balance of Ammonia Recovery Column

To design the ammonia recovery process, we will consider below material balance. This I have taken from my earlier article, “Process Design Calculations for Ammonia Absorber”. We are feeding 16 wt.% ammonia water solution into the ammonia recovery column. This column will operate at 5.0 bar pressure. The column recovers around 95% of ammonia from top and concentration is 97 wt.%. Bottom of column is a waste water stream contains <1.0 wt.% ammonia. In reboiler we will use 9.0 bar saturated steam for column heating and in partial condenser we will use cooling water at 32 ⁰C supply temperature.

Heat Balance for Ammonia Recovery Process

Now we will do the energy balance calculation for reboiler, partial condenser and feed preheater. Subsequently we will estimate the requirement of steam and cooling water also. For this purpose, below are the various parameters and properties.

Reflux rate is 71 kg/h, having 44 wt.% ammonia content. Now we can calculate the heat load on column reboiler at column bottom temperature (i.e., 148 ⁰C) as reference.

Reboiler heat load, Qr = Feed rate*Heat capacity*(148 – 100) + Reflux rate*Latent heat + Reflux rate*Heat capacity*(148 – 45) + Recovered NH3*Heat of solution*ammonia concentration + Recovered NH3*Latent heat of water*moisture content

Qr          = 2851*1.0*(148 – 100) + 71*434 + 71*1.0*(148 – 45) + 433*521*0.97 + 433*538*0.03

= 400798 kcal/h

Partial condenser heat load, Qc = Reflux rate*Latent heat + Reflux rate*Heat capacity*(79 – 45) + Recovered ammonia*Heat capacity*(79 – 45)

Qc          = 71*434 + 71*1.0*(79 – 45) + 433*0.52*(79 – 45) = 40883 kcal/h

Heat load on preheater, Qp = Bottom flow rate*Heat capacity*(148 – 71), after passing through feed preheater column bottom streams cools down to 71 ⁰C.

Qp         = 2404*1.0*(148 – 71) = 185108 kcal/h

We can calculate feed temperature after passing through feed preheater as below

T = Feed temperature at feed preheater inlet + Qp/Feed rate*Heat capacity

T = 35 + 185108/(2851*1.0) = 35 + 65 = 100 ⁰C 

Utility Requirement and Equipment Sizing

We will estimate the steam requirement for ammonia column reboiler.

Ms = Qr / Latent heat of steam @ 9bar = 400798/484.7 = 826.9 kg/h

With 5% heat loss, Ms’ = Ms*1.05 = 868 kg/h

Temperature difference for heat transfer = 175.4 – 148 = 27.4 ⁰C

Over heat transfer for reboiler = 600 kcal/h-m²–⁰C

Estimated reboiler area, Areb = Qr/(600*27.4) = 400789/(600*27.4) = 24.4 m2

Taking 20% excess, reboiler area will be, Areb’ = 24.4*1.20 = 29.3 ~ 30 m2

For partial condenser we can calculate cooling water requirement as below. We will take Condenser cooling water outlet temperature at 38 ⁰C.

Mc = Qc/(Heat capacity*(38 – 32) = 40883/(1.0*6) = 6814 kg/h

LMTD (Log mean temperature difference) = ((79-38) – (45-32))/ln((79-38)/(45-32)) = 24.4 ⁰C

Overall heat transfer coefficient for partial condenser = 150 kcal/h-m²–⁰C

Estimated condenser area will be, Acon = Qc/(LMTD*150) = 40883/(24.4*150) = 11.2 m2

Taking 20% excess, condenser area will be, Acon’ = 11.2*1.20 = 13.44 ~ 15 m2

Feed preheater sizing we can do as follows. First let us calculate LMTD.

LMTD = ((148-100)-(71-35))/ln((148-100)/(71-35)) = 41.7 ⁰C

Overall heat transfer coefficient for feed preheater = 350 kcal/h-m²–⁰C

Estimated feed preheater area will be, Aphe = Qp/(350*LMTD) = 185108/(350*41.7) = 12.7m2

Taking 20% excess, area will be, Aphe’ = 12.7*1.20 = 15.24 ~ 16 m2

Process Controls and Instrumentation

For stable and efficient operation of the ammonia recovery column we need to provide adequate instrumentation and controls. To understand this, you can refer the below figure.

FCV1 is for maintaining constant feed to the ammonia recovery column.

FCV2 will ensure the constant steam flow to the reboiler. Furthermore, we can provide ratio control between feed and steam feed for better controls.

LCV maintain constant level in column bottom. This is critical for stable reboiler operation.

PCV in recovered ammonia gas line will maintain the column pressure.

Remaining instruments like temperature transmitters and pressure transmitters with help us to monitor the performance of the column. In case of any abnormalities, we will get alarms from these transmitters. And we can take necessary actions to restore the process at normal operating conditions.

Conclusion

In this article we discussed the process design and operation of ammonia recovery column. We developed a PFD, material balance and energy balance for the process. Also, we estimated the steam and cooling water requirements for our process. Furthermore, we calculated the surface areas for reboiler, partial condenser and feed preheater.

Apart from this we discussed various instrumentations and controls required for the efficient and stable operation of column.

This article can help you to design the ammonia recovery system for your plant.

Thank you very much for your reading, if you need any other information and clarification feel free to write me.

The post Ammonia Recovery Process Design Calculation appeared first on ChemEnggHelp.

Because of fluidization solid catalyst bed behaves like a fluid and exhibits fluid like properties such as viscosity. And, behaves like a continuous stirred tank reactor or CSTR, this is the basic major advantage over fixed bed reactor. Gas and solids are in intimate contact and well mixed condition. Thus, even for highly exothermic or endothermic reactions, reactor normally operates at completely isothermal conditions. Moreover, catalyst transportation is possible like a fluid from one vessel to another vessel in case of regeneration requirement.

As catalyst inside the reactor vessel is in fine powder form and its particle size distribution ranges among various sizes. Therefore, during the fluidization process coarser particles fall back inside the bed while finer particles comes out with product gases. So, to avoid catalyst loss we provide cyclones to separate this fine powder from the outgoing gases, which return back into the reactor. These cyclones can be inside the reactor or installed outside also.

Minimum Fluidization Velocity

When we continuously increase the gas velocity through as packed bed the pressure drop across bed keep on increasing. At a particular gas flow rate, we will reach a stage when pressure drop across the bed becomes equal to the weight of the bed. This situation we know as a starting of fluidization, and corresponding superficial velocity through vessel is the minimum fluidization velocity. A bed of solid particles exhibits the properties of fluids in this state.

When we further increase gas velocity through the bed it behaves in similar way as we see in case of gas induction in a liquid. So, gas flow rates beyond minimum fluidization velocity flow in form of bubbles and pressure drop remains constant across the bed. This is the fluidization state for gas-solid system and we can use the principles of gas-liquid system to understand the reactor behaviour.

To estimate minimum fluidizing velocity, you can use below equation

Here, ψ = is the dimensionless parameter sphericity measured value ranges from 0.5 to 1, for a granular solid we can use 0.6 (ψ = As/Ap = (surface area of equivalent sphere/surface area of actual particle))

Ԑ_mf = is the void fraction at the point of minimum fluidization velocity and also a dimensionless parameter. And a value Ԑ_mf = 0.5 is typical.

Dp = mean particle diameter we can calculate as  

 , fi is the fraction of particles with diameter Di

g = gravitational constant, μ = gas viscosity, ρ_c = catalyst particle density, ρ_g = gas density

Schematic of Fluidized Bed Reactor

To understand a fluidized bed reactor, you can refer the below figure. In this we can see various major parts comprises Reactor Shell, Catalyst Support Grid, Cyclones, Jacket and Coil for cooling. When reactor is in fluidized state, catalyst level above support grid is known as bed height. The zone above bubbling bed level is called freeboard area. This is the area where heavy catalyst particles separate from outgoing gases by gravity and fall back into the bed. Beyond the freeboard area catalyst particles are pneumatically conveyed and enters into the cyclones. The height above bubbling bed level to reactor outlet is known total disengagement height or TDH.

Fluidized Bed Reactor v/s Fixed Bed Reactor System

Fluidized bed reactors are best suitable for the reactions where we require frequent regeneration of catalyst. Otherwise it is advantageous to go for fixed bed reactor as the conversion will be highest per unit of reactor volume for a given reaction. However, in fixed bed reactors catalyst regeneration is almost impossible because of poor heat transfer. Which leads to localized hot spot generation and runaway conditions in reactor tubes. This results in reactor tube melting and catalyst sintering.

Catalyst Regeneration

In contrast in fluidized bed reactor due to intimate contact of gases with solid and fluidization provides mixed flow conditions. This facilitates almost uniform reactants concentration and temperature throughout the catalyst bed. Which eliminates the possibilities of hot spot formation and provides better temperature control.

Catalyst Handling

Moreover, catalyst replacement in fluidized bed reactor is very easy. Where you can dump the spent catalyst and pneumatically charge the fresh catalyst. While in fixed bed reactor it takes too much time and very tedious job to replace the catalyst. To ensure uniform reactants flow across all the reactor tubes, we need to estimate pressure drop for each and every tube. Also, it very important to ensure proper ratio of inert and catalyst in different segments of the individual tube. Any lapse in this filling process can lead to severe consequences during reactor operation. Therefore, from this point of view fluidized bed reactor is the best option.

Chocking Problems

Furthermore, operation & control of fixed bed reactor is easier than fluidized bed reactor. Because in fluidized bed reactor we need precise control of reactor pressure, flow rates and temperature to ensure efficient fluidization of the catalyst. A pressure disturbance can cause loss of catalyst through cyclones. And this carryover of catalyst with product gases will choke the reactor down stream and you need to shutdown the plant for cleaning of equipment, such as venturi scrubber, condenser, connecting pumps, filters and piping. In case of inlet gases flow interruption catalyst may seep below the catalyst support grid and will chock the bottom of reactor. We don’t see these kinds of problems in fixed bed reactor system, therefore comparatively easy to operate.

Maintenance

From maintenance point of view fixed bed reactors are better option where there are no moving parts inside. Once you fix the reactor it will keep on running without any mechanical failure. While in the case of fluidized bed reactor fine catalyst power is continuously remain in dynamic state. This movement of catalyst causes erosion of reactor internal parts including cyclone inlet, reactor shell and catalyst support grid. Generally, cyclone and support grid nozzles require frequent replacements.

In fluidized bed reactor because of fluidization of catalyst we also face dynamic loading on plant structure. Therefore, to avoid excess vibrations and damage of plant structure we should take care for this dynamic loading during steel structure designing.

Operation & Controls of Fluidized Bed Reactor System

As we discussed above fluidized bed reactor is most suitable where we require continuous regeneration of the catalyst. During reaction step coke forms and deposits on catalyst surface and inside the pores. This coke deposition decreases the activity of the catalyst which reduces the conversion of the reaction. Therefore, to maintain constant conversion and capacity from reactor we need to regenerate the catalyst continuously. We use air for the coke generation, which takes place around 550 – 600 ⁰C.

The major application of fluidized bed reactor you can see in Catalytic Cracker, which the heart of the petroleum refineries. In cracker catalyst particle facilitates the breaking of large molecules in smaller useful molecules of gasoline, diesel, fuel oil, etc. This incoming crude vapour keeps the cracker catalyst in fluidized state. During this reaction coke formation takes place which deposits on the catalyst particle surface and deactivates it. To regenerate it we continuously circulate this catalyst in another vessel to reactivate it using air. This vessel is known as regenerator and coke combustion takes place with air; this air keeps the catalyst bed in fluidized condition. You can refer below figure to understand the catalytic cracking process.

During operation pressure drop across catalyst support grid is important for efficient fluidization. Simultaneously, pressure drop between cracker and regenerator is very critical for smooth circulation of the catalyst.

In fluidized bed reactors cyclone efficiency is very important. Wrong cyclone design will cause of fine particles loss from the catalyst bed. At low fine % gas bubbles will be of bigger sizes and will reduce the contact surface area between solid and gas. Subsequently, this will negatively impact the raw materials conversion. Therefore, to maintain the adequate fines in fluidizing bed is important for smaller size bubbles formation.

Cyclone dip leg design is also very important to minimize the catalyst loss. A wrong diameter of dip leg will allow the channelling of reactants gases from the cyclone dip leg and enhance catalyst loss also.

Conclusion

In this article we discussed about the fluidized bed reactor system. How it works and what are the various advantages and disadvantages in comparison with a fixed bed reactor. Design of fluidized bed is based on minimum fluidization velocity. This we use to estimate the reactor diameter, in actual fluidized bed reactors operates at a higher velocity than minimum fluidization velocity. The actual fluidization velocity can be around 30 to 70 times of minimum fluidization velocity.

Furthermore, we must see for the real-time data analysis of the fluidized bed reactors. This will give us the insight for better operation and improved yield. We can develop Machine learning models to predict the cyclone & catalyst support grid failures.

Thanks for reading and looking forward for your comments and feed backs.

The post Fluidized Bed Reactor appeared first on ChemEnggHelp.