Program for North American Mobility in Higher Education (NAMP)

Created atCreated atÉcole Polytechnique de École Polytechnique de

Montréal &Montréal &Universidad de GuanajuatoUniversidad de Guanajuato

PIECEPIECEProgram for North American Mobility In Higher EducationProgram for North American Mobility In Higher Education

Rev:2.3Rev:2.3

Program for North American Mobility Program for North American Mobility in Higher Education (NAMP)in Higher Education (NAMP)

Introducing Process Integration for Introducing Process Integration for Environmental Control in Engineering Environmental Control in Engineering

Curricula (PIECE)Curricula (PIECE)

Module 8: Introduction to Process Module 8: Introduction to Process Integration – Tier IIIIntegration – Tier III

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Module 8: Introduction to Process Integration

Project Summary

Objectives Objectives Create web-based modules to assist universities to Create web-based modules to assist universities to address the introduction to Process Integration into address the introduction to Process Integration into engineering curriculaengineering curriculaMake these modules widely available in each of the Make these modules widely available in each of the participating countriesparticipating countries

Participating institutionsParticipating institutions

Two universities in each of the three countries Two universities in each of the three countries (Canada, Mexico and the USA)(Canada, Mexico and the USA)Two research institutes in different industry sectors: Two research institutes in different industry sectors: petroleum (Mexico) and pulp and paper (Canada)petroleum (Mexico) and pulp and paper (Canada)Each of the six universities has sponsored 7 Each of the six universities has sponsored 7 exchange students during the period of the grant exchange students during the period of the grant subsidised in part by each of the three countries’ subsidised in part by each of the three countries’ governmentsgovernments

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What is the structure of this module?What is the structure of this module?

All Modules are divided into 3 tiers, each with a specific goal:All Modules are divided into 3 tiers, each with a specific goal:Tier I: Background InformationTier I: Background InformationTier II: Case Study ApplicationsTier II: Case Study ApplicationsTier III: Open-Ended Design ProblemTier III: Open-Ended Design Problem

These tiers are intended to be completed in that particular These tiers are intended to be completed in that particular order. Students are quizzed at various points to measure order. Students are quizzed at various points to measure their degree of understanding, before proceeding to the next their degree of understanding, before proceeding to the next level.level.

Each tier contains a statement of intent at the beginning and Each tier contains a statement of intent at the beginning and a quiz at the end.a quiz at the end.

Structure of Module 8

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What is the purpose of this module?What is the purpose of this module?

It is the intent of this module to cover the basic aspects of It is the intent of this module to cover the basic aspects of Process Integration MethodsProcess Integration Methods and and ToolsTools, and to place , and to place Process IntegrationProcess Integration into a broad perspective. It is into a broad perspective. It is identified as a pre-requisite for other modules related to identified as a pre-requisite for other modules related to the learning of the learning of Process Integration.Process Integration.

Purpose of Module 8

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Tier IIIOpen-ended problem

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Tier III: Objective

Tier III: Statement of intentTier III: Statement of intentThe goal of this tier is to The goal of this tier is to solve a real-life application of solve a real-life application of Process Integration, in which the student must interpret Process Integration, in which the student must interpret the results obtained from a range of Process Integration the results obtained from a range of Process Integration tools. At the end of Tier III, the student should be able to tools. At the end of Tier III, the student should be able to identify the following:identify the following:

Benefits of the use of Process Integration toolsBenefits of the use of Process Integration toolsPotential cost saving opportunities from the use of Potential cost saving opportunities from the use of Process Integration toolsProcess Integration toolsEnvironmental impact reduction resulting from the Environmental impact reduction resulting from the application of Process Integration toolsapplication of Process Integration toolsHow the application of Process Integration tools can How the application of Process Integration tools can be used to obtain an operable processbe used to obtain an operable process

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The Kraft pulping processThe Kraft pulping processThe basic features of a Kraft pulping process are shown on the next slide. Wood The basic features of a Kraft pulping process are shown on the next slide. Wood chips (containing 50% water) are conveyed from a surge hopper to a chips (containing 50% water) are conveyed from a surge hopper to a presteaming unit to facilitate subsequent impregnation of the chips with presteaming unit to facilitate subsequent impregnation of the chips with chemicals. A high-pressure feeder transfers the chips from the presteaming chemicals. A high-pressure feeder transfers the chips from the presteaming vessel to the digester. In the digester, the wood chips are “cooked” using white vessel to the digester. In the digester, the wood chips are “cooked” using white liquor (a mixture of cooking chemicals including NaOH, Naliquor (a mixture of cooking chemicals including NaOH, Na22S, NaS, Na22COCO3 3 and water) and water) to solubilize the lignin in the wood chips. In the cooking process, methanol is to solubilize the lignin in the wood chips. In the cooking process, methanol is produced. Following digestion of the lignin, the cooking chemicals are washed produced. Following digestion of the lignin, the cooking chemicals are washed out of the pulp. A countercurrent multistage washing unit is utilized to minimize out of the pulp. A countercurrent multistage washing unit is utilized to minimize the carryover of chemicals with the pulp. The residual chemicals from the the carryover of chemicals with the pulp. The residual chemicals from the pulping process are called the weak black liquor. The black liquor contains pulping process are called the weak black liquor. The black liquor contains sodium salts (hydroxide, sulphide, carbonate, chloride, sulphite and sulphate), sodium salts (hydroxide, sulphide, carbonate, chloride, sulphite and sulphate), dissolved lignin, methanol and water. Before the outlet to the digester is fed to dissolved lignin, methanol and water. Before the outlet to the digester is fed to the washers, the cooked pulp and liquor are passed to a blow tank where the the washers, the cooked pulp and liquor are passed to a blow tank where the pulp is separated from the weak black liquor which is fed to a recovery system pulp is separated from the weak black liquor which is fed to a recovery system for conversion to white liquor. The first step in recovery is concentration of the for conversion to white liquor. The first step in recovery is concentration of the weak black liquor via multiple effect evaporators. The concentrated solution is weak black liquor via multiple effect evaporators. The concentrated solution is sprayed in a recovery furnace. The evaporation process results in the sprayed in a recovery furnace. The evaporation process results in the generation of a large amount of combined condensate which is classified as a generation of a large amount of combined condensate which is classified as a wastewater stream and of gaseous waste whose primary pollutant is Hwastewater stream and of gaseous waste whose primary pollutant is H22S. The S. The smelt from the furnace is dissolved in water to form green liquor which is smelt from the furnace is dissolved in water to form green liquor which is reacted with lime (CaO) to produce white liquor and calcium carbonate “mud”. reacted with lime (CaO) to produce white liquor and calcium carbonate “mud”. The recovered white liquor is mixed with make-up materials and recycled to the The recovered white liquor is mixed with make-up materials and recycled to the digester. The calcium carbonate mud is thermally decomposed in a kiln to digester. The calcium carbonate mud is thermally decomposed in a kiln to produce lime which is used in the causticizing reaction. There are several produce lime which is used in the causticizing reaction. There are several gaseous wastes emitted from the process, some of which can be used for steam gaseous wastes emitted from the process, some of which can be used for steam generation or cogeneration.generation or cogeneration.

Tier III – Problem Statement

Reference: El-Halwagi, M. M., Reference: El-Halwagi, M. M., Pollution Prevention through Process Integration: Systematic Design Tools. . Academic Press, 1997.Academic Press, 1997.

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Slaking &

Causticizing

Settling &

Filtration

Digester

Blow Tank

Recovery

Furnace

Dissolving

Tank

Lime Kiln

Mu

ltip

le E

ffect

Evap

ora

tors

Lime

Recovered White Liquor

Pulp to further

processing

GasesOff Gas

Wood Chips

SteamWeak

Black Liquor

Steam

Strong Black Liquor

Condensate

Flue Gas

Smelt

Off Gas

Water

Green Liquor

Calcium Carbonat

e

Air

Gases

Gaseous Waste

Washers

Reference: El-Halwagi, M. M., Pollution Prevention through Process Integration: Systematic Design Tools. Academic Press, 1997.Reference: El-Halwagi, M. M., Pollution Prevention through Process Integration: Systematic Design Tools. Academic Press, 1997.

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Wastewater treatment in the Kraft pulping processWastewater treatment in the Kraft pulping process

Pulp and paper mills employ high levels of fresh water that lead to the generation of Pulp and paper mills employ high levels of fresh water that lead to the generation of a significant amount of aqueous effluent. Therefore, the objective of optimizing water a significant amount of aqueous effluent. Therefore, the objective of optimizing water usage and wastewater discharge presents a major challenge to the industry. Due to usage and wastewater discharge presents a major challenge to the industry. Due to the direct contact of water with various species, the aqueous streams are laden with the direct contact of water with various species, the aqueous streams are laden with various compounds including methanol, non-process elements and organic and various compounds including methanol, non-process elements and organic and inorganic species. Methanol is classified as a high priority pollutant for the pulping inorganic species. Methanol is classified as a high priority pollutant for the pulping industry. In addition, it may provide a source of revenue if properly recovered.industry. In addition, it may provide a source of revenue if properly recovered.

Methanol can be found in most wastewater streams of the Kraft pulping process Methanol can be found in most wastewater streams of the Kraft pulping process particularly in the condensate leaving the multiple effect evaporators and the particularly in the condensate leaving the multiple effect evaporators and the condensers used to condensate the steam from the presteaming unit before the condensers used to condensate the steam from the presteaming unit before the wood chips are taken to the digester. All the wastewater streams are treated using wood chips are taken to the digester. All the wastewater streams are treated using biotreatment and then discharged to the river. Any stream discharged to the river biotreatment and then discharged to the river. Any stream discharged to the river should not have a methanol composition which exceeds 15 ppmw. The following should not have a methanol composition which exceeds 15 ppmw. The following information is available for the biotreatment facility:information is available for the biotreatment facility:

• acceptable methanol composition entering biotreatment acceptable methanol composition entering biotreatment << 1.000 ppmw 1.000 ppmw• average outlet methanol composition = 15 ppmwaverage outlet methanol composition = 15 ppmw• biotreatment operating cost = 0.11*biotreatment operating cost = 0.11*MM + 0.0013* + 0.0013*G G where where M M is the mass load is the mass load

(kg(kg//h) of methanol and h) of methanol and GG is the flowrate of wastewater (kg is the flowrate of wastewater (kg//h)h)


Reference: El-Halwagi, M. M., Pollution Prevention through Process Integration: Systematic Design Tools. Reference: El-Halwagi, M. M., Pollution Prevention through Process Integration: Systematic Design Tools. Academic Press, 1997.Academic Press, 1997.

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Wastewater treatment in the Kraft pulping process (2)Wastewater treatment in the Kraft pulping process (2)

The amount of methanol in the wastewater could be reduced using air stripping and The amount of methanol in the wastewater could be reduced using air stripping and recovered from aqueous streams to provide methanol sales that are higher than recovered from aqueous streams to provide methanol sales that are higher than recovery costs. The flowrate of air is determined as follows:recovery costs. The flowrate of air is determined as follows:

LL = 0.5* = 0.5*ƒƒ**GG

Where Where LL and and GG are the mass flowrates (kg are the mass flowrates (kg//h) of air and wastewater, respectively, and h) of air and wastewater, respectively, and ƒ is the fractional mass removal of methanol from water by stripping. The operating ƒ is the fractional mass removal of methanol from water by stripping. The operating cost for air stripping is given by the following relationship:cost for air stripping is given by the following relationship:

Operating Cost Operating Cost (US$(US$//h) = 0.003*h) = 0.003*LL (kg air (kg air//h)h)

This cost includes air compression and methanol condensation.This cost includes air compression and methanol condensation.

The wastewater treatment plant operator also has problems predicting when the The wastewater treatment plant operator also has problems predicting when the treatment process will go from one operating regime to another or when the process treatment process will go from one operating regime to another or when the process will produce water with above permitted limits concentrations of methanol and other will produce water with above permitted limits concentrations of methanol and other pollutants. He disposes of the treatment facility´s last three years of operating data pollutants. He disposes of the treatment facility´s last three years of operating data but does not know how to interpret such amounts of information.but does not know how to interpret such amounts of information.


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Wastewater treatment in the Kraft pulping process (3)Wastewater treatment in the Kraft pulping process (3)

Along with methanol as one of the main pollutants found in Kraft pulp mill aqueous Along with methanol as one of the main pollutants found in Kraft pulp mill aqueous effluents, other organic and inorganic compounds are found. These include effluents, other organic and inorganic compounds are found. These include chloroform, formaldehyde, phenol and others, depending on the mill and process chloroform, formaldehyde, phenol and others, depending on the mill and process used. Phenol is of concern primarily because of its toxicity, oxygen depletion and used. Phenol is of concern primarily because of its toxicity, oxygen depletion and turbidity. In addition, phenol can cause objectionable taste and odour in fish flesh turbidity. In addition, phenol can cause objectionable taste and odour in fish flesh and potable water.and potable water.

Several techniques can be used to separate phenol. Three external technologies are Several techniques can be used to separate phenol. Three external technologies are here considered for the removal of phenol. These processes include adsorption here considered for the removal of phenol. These processes include adsorption using activated carbon, ion exchange using a polymeric resin and stripping using using activated carbon, ion exchange using a polymeric resin and stripping using air.air.

The operating costs for each method comprise cost of make-up and cost of The operating costs for each method comprise cost of make-up and cost of regeneration. For activated carbon, steam is used to regenerate the mass-regeneration. For activated carbon, steam is used to regenerate the mass-separating agent while caustic soda (NaOH) is used for the regeneration of the ion separating agent while caustic soda (NaOH) is used for the regeneration of the ion exchange resin. In the case of air stripping, the gaseous stream leaving the mass-exchange resin. In the case of air stripping, the gaseous stream leaving the mass-exchange unit cannot be discharged to the atmosphere owing to air-quality exchange unit cannot be discharged to the atmosphere owing to air-quality regulations. Hence, the air leaving the separation unit is fed to a phenol-recovery regulations. Hence, the air leaving the separation unit is fed to a phenol-recovery unit in which a refrigerant is used to condense phenol. The operating cost related to unit in which a refrigerant is used to condense phenol. The operating cost related to each technology is thus 0.737 US$, 1.150 US$ and 2.069 US$ per kg of removed each technology is thus 0.737 US$, 1.150 US$ and 2.069 US$ per kg of removed phenol for activated carbon, ion exchange resin and air stripping respectively.phenol for activated carbon, ion exchange resin and air stripping respectively.


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Energy in the Kraft pulping processEnergy in the Kraft pulping process

The Kraft pulping process is a very energy-intensive process: electricity end-uses The Kraft pulping process is a very energy-intensive process: electricity end-uses common to all pulp and paper mills include pumping, air-handling, and lighting. In common to all pulp and paper mills include pumping, air-handling, and lighting. In addition, steam needs and the large number of process streams makes this sector addition, steam needs and the large number of process streams makes this sector of the industry a good candidate for improved heat integration. Black liquor of the industry a good candidate for improved heat integration. Black liquor concentration is usually the biggest single steam using operation in a Kraft pulp mill. concentration is usually the biggest single steam using operation in a Kraft pulp mill. Evaporators installed in the 1960s and 1970s were built with four or five effects, Evaporators installed in the 1960s and 1970s were built with four or five effects, whereas most Kraft mills today use five or six effect evaporators, with a whereas most Kraft mills today use five or six effect evaporators, with a concentrator to further increase solids content. Firing the recovery boiler with the concentrator to further increase solids content. Firing the recovery boiler with the black liquor at higher solids content improves overall boiler performance and is a black liquor at higher solids content improves overall boiler performance and is a general trend in the industry.general trend in the industry.

To counter this energy consumption problem, a Kraft pulp mill uses biomass. In fact, To counter this energy consumption problem, a Kraft pulp mill uses biomass. In fact, in addition to being the feedstock for pulp and paper production, biomass is also a in addition to being the feedstock for pulp and paper production, biomass is also a major energy resource for the industry. The industry also has access to residues of major energy resource for the industry. The industry also has access to residues of pulpwood harvesting, some of which can be removed from the forest on a pulpwood harvesting, some of which can be removed from the forest on a sustainable basis. All black liquor and most mill residues are used at mill sites to sustainable basis. All black liquor and most mill residues are used at mill sites to fuel cogeneration systems, providing steam and electricity for on-site use. fuel cogeneration systems, providing steam and electricity for on-site use. Cogeneration also known as Combined Heat and Power (CHP) is the simultaneous Cogeneration also known as Combined Heat and Power (CHP) is the simultaneous production of electricity and useful heat from the same fuel or energy. A typical production of electricity and useful heat from the same fuel or energy. A typical cogeneration system consists of an engine, steam turbine, or combustion turbine cogeneration system consists of an engine, steam turbine, or combustion turbine that drives an electrical generator. A waste heat exchanger recovers waste heat that drives an electrical generator. A waste heat exchanger recovers waste heat from the engine and/or exhaust gas to produce hot water or steam. from the engine and/or exhaust gas to produce hot water or steam.

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Energy in the Kraft pulping process (2)Energy in the Kraft pulping process (2)

Cogeneration produces a given amount of electric power and process heat with 10% Cogeneration produces a given amount of electric power and process heat with 10% to 30% less fuel than it takes to produce the electricity and process heat separately. to 30% less fuel than it takes to produce the electricity and process heat separately. Facilities with cogeneration systems use them to produce their own electricity, and Facilities with cogeneration systems use them to produce their own electricity, and use the unused excess (waste) heat for process steam, hot water heating, space use the unused excess (waste) heat for process steam, hot water heating, space heating, and other thermal needs. They may also use excess process heat to heating, and other thermal needs. They may also use excess process heat to produce steam for electricity production. produce steam for electricity production. In the chemical recovery, steam plant and In the chemical recovery, steam plant and cogeneration areas, pulping liquor solids, purchased and self-generated woodwaste, cogeneration areas, pulping liquor solids, purchased and self-generated woodwaste, primary clarifier sludge from the wastewater treatment plant, and knots are burned primary clarifier sludge from the wastewater treatment plant, and knots are burned to recover cooking chemicals and to produce energy. to recover cooking chemicals and to produce energy. Spent pulping liquors account Spent pulping liquors account for over 70% of the biomass-derived fuels used in the pulp and paper industry for over 70% of the biomass-derived fuels used in the pulp and paper industry today. today. In the recovery process, the resulting strong black liquor from the evaporators is In the recovery process, the resulting strong black liquor from the evaporators is sprayed into the recovery boiler where the organic content in the liquor is burned, sprayed into the recovery boiler where the organic content in the liquor is burned, releasing energy and producing steam for use in the mill. Upon combustion, the releasing energy and producing steam for use in the mill. Upon combustion, the inorganic portion of the strong black liquor produces a flue gas. inorganic portion of the strong black liquor produces a flue gas. The electricity-to-heat production ratio for a conventional back-pressure steam The electricity-to-heat production ratio for a conventional back-pressure steam turbine cogeneration system ranges from 40-60 kWh/GJ, which is relatively well-turbine cogeneration system ranges from 40-60 kWh/GJ, which is relatively well-matched to the steam and electricity needs at older Kraft mills. Much higher matched to the steam and electricity needs at older Kraft mills. Much higher electricity-to-heat ratios are possible using biomass and black liquor cogeneration electricity-to-heat ratios are possible using biomass and black liquor cogeneration technologies based on gas turbines rather than steam turbines. Commercially-technologies based on gas turbines rather than steam turbines. Commercially-aimed development of technologies for converting black liquor or biomass residues aimed development of technologies for converting black liquor or biomass residues into combustible fuel gas is ongoing, along with the cleanup systems that would be into combustible fuel gas is ongoing, along with the cleanup systems that would be needed to enable use of the gas in gas turbine cycles.needed to enable use of the gas in gas turbine cycles.

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Tier III – Questions

Question 1. Wastewater treatment in the Kraft pulping Question 1. Wastewater treatment in the Kraft pulping processprocess

Which Process Integration tools could be used to address all the issues Which Process Integration tools could be used to address all the issues presented in the methanol related slides? Define the steps in the presented in the methanol related slides? Define the steps in the methodology you would use to answer the following points:methodology you would use to answer the following points:

(A)(A) Methanol minimization in the wastewater streams as well as reduced Methanol minimization in the wastewater streams as well as reduced water usage and reduced wastewater dischargewater usage and reduced wastewater discharge

(B)(B) Trade-off between minimization of operating costs related to the Trade-off between minimization of operating costs related to the elements stated in (A) and benefits resulting from the recuperation of elements stated in (A) and benefits resulting from the recuperation of methanolmethanol

(C)(C) Interpretation and use of process operating data to help the treatment Interpretation and use of process operating data to help the treatment plant operator obtain better control of the operation of the wastewater plant operator obtain better control of the operation of the wastewater treatment planttreatment plant

Question 2. Wastewater treatment in the Kraft pulping Question 2. Wastewater treatment in the Kraft pulping process (2)process (2)

Using your knowledge of Process Integration tools, describe the Using your knowledge of Process Integration tools, describe the methodology that could be used to choose the best mass-separating methodology that could be used to choose the best mass-separating agent to treat the waste streams of phenol in this Kraft pulp and paper agent to treat the waste streams of phenol in this Kraft pulp and paper mill. mill.

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Tier III – Questions

Question 3. Energy in the Kraft pulping process Question 3. Energy in the Kraft pulping process

With the knowledge of Process Integration acquired over the last two With the knowledge of Process Integration acquired over the last two tiers, propose a methodology that would help identify the energy tiers, propose a methodology that would help identify the energy savings possibilities as well as the potential for cogeneration in a Kraft savings possibilities as well as the potential for cogeneration in a Kraft pulp mill. Elaborate on each of the steps taken to conduct such a study pulp mill. Elaborate on each of the steps taken to conduct such a study and remember to include in your proposition the impact of your solution and remember to include in your proposition the impact of your solution on the environment. on the environment.

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End of Tier III

This is the end of Module 8. Please submit your report to This is the end of Module 8. Please submit your report to your professor for grading.your professor for grading.

We are always interested in suggestions on how to improve We are always interested in suggestions on how to improve the course. You may contact us as the course. You may contact us as http://process-http://process-integration.tamu.edu/integration.tamu.edu/

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Program for North American Mobility in Higher Education (NAMP)