Technical Paper
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Technical Paper as PDF for free.
More details
- Words: 1,714
- Pages: 4
The vital link
THE GASKET The operational cycle and hence the availability of a plate heat exchanger is highly dependent on the gaskets. Which makes the choice of gaskets decisive. This folder tells you more about materials, lifetime and applications.
T
Gaskets for conventional plate heat exchangers are made of various elastic and formable materials, such as rubber. Experts can testify that rubber is a complex, high-molecular material composed of a number of different substances.
he main component of rubber is rubber polymer, which occurs in various forms. The most common types of polymer are pure hydrocarbons such as EPDM, IIR or NR, which are not oilresistant, substituted hydrocarbons in which a hydrogen atom is replaced by e.g. a chlorine or fluorine atom, as in NBR, CR, CSM or FPM, all of which are highly oilresistant, or non-hydrocarbons, such as silicon or polyphosphazene, which have varying resistance to oil. However, polymers do not become elastic until they undergo vulcanization, when the chains of molecules are cross-linked into the three-dimensional network that is typical of polymers.
Structure of rubber In addition to polymers, rubber comprises a number of other raw materials: — Vulcanization chemicals such as sulphur, organic resins and organic peroxides. These substances bind the rubber polymer to a three-dimensional network which gives the rubber its elastic properties. —Fillers, i.e. extenders and reinforcing components that enhances such physical properties of the rubber as hardness and strength. Carbon black is widely used as a filler and also makes the rubber black. —Anti-degradants, which delay aging of the rubber when it comes in contact with aggressive substances such as oxygen or ozone. —Components that facilitate handling and manufacturing, e.g. those that make the rubber softer and more pliable, and thus easier to work. The quality of a gasket is related to the proportions of the raw materials. The quantity of polymer is important and is usually around 50%. Cheaper products often have less rubber, sometimes no more than 20%, but more fillers
and softeners, such as lampblack or various types of oils. Cheap rubber therefore ages faster and is less effective as a sealant.
Number of components A number of different raw materials and chemicals are available for production of rubber. This means that the development process demands long experience and special expertise. The number of substances that are available for making a new type of rubber illustrates the complexity of developing rubber: - 100 grades of EPDM polymers - 150 different nitrile polymers - 50 fluorocarbon polymers - 20 butyl polymers - 600 vulcanization chemicals - 200 fillers - 300 anti-degradants - 300 processing aids
Laboratory work Alfa Laval Thermal maintains an intensive and continuous development program aimed at improving the performance of our plate heat exchangers. This program consists of six primary phases: 1. Study of literature and previous experiments, which can take up to 4 months. 2. The 10 rubber materials that are most promising in theory are chosen and subjected to chemical and mechanical stress, e.g. oxygen and stretching. This phase may take up to 5 months. 3. The materials with the best results are then tested in plate heat exchangers in the laboratory for as long as 1 year. 4. The feasibility of producing the rubber industrially is then evaluated, which may take up to 2 months.
Long lifetime Developing a specific gasket material calls for time and money. But these resources represent an investment that pays off for the user in terms of reliable operation.
5. The two best gasket materials are then tested in one or more practical applications for at least 1 year. This clarifies how the materials perform in terms of operation, service, cleaning and other real-world parameters. 6. The rubber material with the best results is approved for manufacture. The compound must not be modified and in most cases must not be divulged without written approval from Alfa Laval.
Manufacturing expertise In summary, rubber consists of a number of different substances depending on the application, such as a squash ball, jogging shoes or a gasket for a plate heat exchanger. The important thing to remember is that a gasket from one supplier is seldom identical to a gasket from another supplier, although the gaskets may have the same designation. This means that a nitrile gasket from one supplier does not necessarily have the same properties as a nitrile gasket from another source. It takes a long time to acquire the expertise required for identifying the precise requirements of various media and applications in terms of gaskets. Developing a specific gasket material calls for time and money. But these resources represent an investment that pays off for the user in terms of reliable operation.
LADISLAV NOVAK Ph. D., Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden. Materials Laboratory Manager, Alfa Laval Thermal, Lund, Sweden.
Quality means reliability. That s why it s vital to select the right gasket for a plate heat exchanger. The main point is to avoid downtime! Low-quality gaskets result in reduced capacity for a plate heat exchanger. There s no question about that. And it s just as obvious that a quality gasket means higher reliability. But over time, even a quality gasket becomes less elastic and loses some of its capability as a sealant. In the end, aging leads to leaks and downtime. Aging results from exposure to oxygen, high temperatures and other factors. That s why the right gasket should provide maximum resistance to these factors. And the right gasket is never a question of a standard solution.
Resilience A new gasket has impressive resilience, exactly like a young person looking forward to a long life. The gasket expands and fills its groove in order to seal in the media that flow through the exchanger. This is the condition that we want to maintain. But since rubber is an organic material, it is affected by its ambient environment —in other words, it ages. This is unavoidable. But there are ways to prolong the life of rubber. First of all, this calls for investing in the right type of gasket. Since the plates have deep channels, a design such as an O-ring can t be used, as it is best fitted to serve as a plug. Instead, the right gasket has to be capable of compression in order to resist the stresses and forces that the flow of media can generate. Secondly, the right gasket materials must be selected, and this requires comprehensive expertise in applications and materials. Some applications generate less wear, such as
Long lifetime continued
water/water at low temperatures. A gasket in an exchanger with this type of duty can last for many years without leaking. But there are other applications which quickly reveal the quality of a gasket in no uncertain terms. The process industry is one example. In this sector, heat exchangers handle aggressive media such as lye and acids. If the temperature of these media is also high, the stress on the gaskets can be very great.
Some applications require a plate heat exchanger with gaskets. A quality gasket gives higher reliability.
EPDM and nitrile rubber The two most commonly used materials for gaskets are EPDM and nitrile rubber. EPDM is often used in the processing industry and shows impressive resistance to corrosive media. It is also used in heat exchangers where media temperatures are high, as nitrile rubber is sensitive to these. But this does not mean that EPDM is a general solution for difficult applications.
Limitations It s often said that lik e dissolves like , and in many cases this means that EPDM reacts with oil, swells and then cracks. EPDM can thus not be used in applications such as oil platforms. Although these applications involve very high temperatures, nitrile gaskets are used nevertheless, thanks to a specially developed variant of nitrile rubber. This shows that there is no standardized solution when it comes to selecting a gasket, which in turn means that each compound for gasket material also has to be unique. The compounds are developed with reference to the type of media in the heat exchanger and the ambient environment.
Gasket-free? It could be asked why plate heat exchangers with gaskets are used in the first place. There are gasketfree units that can be cleaned easily with CIP (Cleaning-In-Place) systems. A CIP system is connected to the heat exchanger, which is then washed with a cleaning agent that dissolves scale, among other things. In other words, a CIP system enables cleaning without the need to open the heat exchanger.
One reason for choosing plate heat exchangers with gaskets is that specific applications require units that must be opened in order to clean them. They cannot be maintained in acceptable condition with CIP alone, but must be cleaned mechanically because the channels are blocked by materials that are difficult to dissolve, such as sand, clay or various types of salts. It is possible to dislodge these materials with chemicals, but this involves a risk of attacking the plates as well. Another reason is that plate heat exchangers with gaskets are more flexible. They can easily be opened and reconfigured. They have a broad range of applications, and investing in a gasket-free unit is not always necessary, since gasketed exchangers have enough capacity and are also compact. In addition, they are easy to monitor in terms of dirt, scale and blockages.
Gasket data base Selecting the right gasket is not easy. That s why Alfa Laval s gasket specialists have created a data base comprising all available information on rubber and gasket materials. The computerized data base has been created in order to provide customers with information that is as precise as possible. It responds to questions regarding the media in the heat exchanger and the pressure and temperatures to which the gasket will be exposed. The data base then immediately generates recommendations for appropriate gaskets.
Valutech Inc Tel: Avenue, (905) 940-0961 Toronto 101 Milner Avenue, Ontario M1S 4S6 ¥ Edmonton 4727 - 68th Alberta T6N 2N2 70 Esna Park ¥ Drive, 3 299-3535 Fax: (905) Tel.: (416) 299-6101 ¥ Toll Free 1-888-ALFACAN Fax:Unit (416) ¥ 940-0983 www.alfalaval.ca Markham, Ontario, L3R 6E7
E-Mail: [email protected]
Heat Exchangers • Process Equipment • Control Valves • Steam Traps • Mixers • Industrial Valves • Technical Services
THE GASKET The operational cycle and hence the availability of a plate heat exchanger is highly dependent on the gaskets. Which makes the choice of gaskets decisive. This folder tells you more about materials, lifetime and applications.
T
Gaskets for conventional plate heat exchangers are made of various elastic and formable materials, such as rubber. Experts can testify that rubber is a complex, high-molecular material composed of a number of different substances.
he main component of rubber is rubber polymer, which occurs in various forms. The most common types of polymer are pure hydrocarbons such as EPDM, IIR or NR, which are not oilresistant, substituted hydrocarbons in which a hydrogen atom is replaced by e.g. a chlorine or fluorine atom, as in NBR, CR, CSM or FPM, all of which are highly oilresistant, or non-hydrocarbons, such as silicon or polyphosphazene, which have varying resistance to oil. However, polymers do not become elastic until they undergo vulcanization, when the chains of molecules are cross-linked into the three-dimensional network that is typical of polymers.
Structure of rubber In addition to polymers, rubber comprises a number of other raw materials: — Vulcanization chemicals such as sulphur, organic resins and organic peroxides. These substances bind the rubber polymer to a three-dimensional network which gives the rubber its elastic properties. —Fillers, i.e. extenders and reinforcing components that enhances such physical properties of the rubber as hardness and strength. Carbon black is widely used as a filler and also makes the rubber black. —Anti-degradants, which delay aging of the rubber when it comes in contact with aggressive substances such as oxygen or ozone. —Components that facilitate handling and manufacturing, e.g. those that make the rubber softer and more pliable, and thus easier to work. The quality of a gasket is related to the proportions of the raw materials. The quantity of polymer is important and is usually around 50%. Cheaper products often have less rubber, sometimes no more than 20%, but more fillers
and softeners, such as lampblack or various types of oils. Cheap rubber therefore ages faster and is less effective as a sealant.
Number of components A number of different raw materials and chemicals are available for production of rubber. This means that the development process demands long experience and special expertise. The number of substances that are available for making a new type of rubber illustrates the complexity of developing rubber: - 100 grades of EPDM polymers - 150 different nitrile polymers - 50 fluorocarbon polymers - 20 butyl polymers - 600 vulcanization chemicals - 200 fillers - 300 anti-degradants - 300 processing aids
Laboratory work Alfa Laval Thermal maintains an intensive and continuous development program aimed at improving the performance of our plate heat exchangers. This program consists of six primary phases: 1. Study of literature and previous experiments, which can take up to 4 months. 2. The 10 rubber materials that are most promising in theory are chosen and subjected to chemical and mechanical stress, e.g. oxygen and stretching. This phase may take up to 5 months. 3. The materials with the best results are then tested in plate heat exchangers in the laboratory for as long as 1 year. 4. The feasibility of producing the rubber industrially is then evaluated, which may take up to 2 months.
Long lifetime Developing a specific gasket material calls for time and money. But these resources represent an investment that pays off for the user in terms of reliable operation.
5. The two best gasket materials are then tested in one or more practical applications for at least 1 year. This clarifies how the materials perform in terms of operation, service, cleaning and other real-world parameters. 6. The rubber material with the best results is approved for manufacture. The compound must not be modified and in most cases must not be divulged without written approval from Alfa Laval.
Manufacturing expertise In summary, rubber consists of a number of different substances depending on the application, such as a squash ball, jogging shoes or a gasket for a plate heat exchanger. The important thing to remember is that a gasket from one supplier is seldom identical to a gasket from another supplier, although the gaskets may have the same designation. This means that a nitrile gasket from one supplier does not necessarily have the same properties as a nitrile gasket from another source. It takes a long time to acquire the expertise required for identifying the precise requirements of various media and applications in terms of gaskets. Developing a specific gasket material calls for time and money. But these resources represent an investment that pays off for the user in terms of reliable operation.
LADISLAV NOVAK Ph. D., Chemical Engineering, Chalmers University of Technology, Gothenburg, Sweden. Materials Laboratory Manager, Alfa Laval Thermal, Lund, Sweden.
Quality means reliability. That s why it s vital to select the right gasket for a plate heat exchanger. The main point is to avoid downtime! Low-quality gaskets result in reduced capacity for a plate heat exchanger. There s no question about that. And it s just as obvious that a quality gasket means higher reliability. But over time, even a quality gasket becomes less elastic and loses some of its capability as a sealant. In the end, aging leads to leaks and downtime. Aging results from exposure to oxygen, high temperatures and other factors. That s why the right gasket should provide maximum resistance to these factors. And the right gasket is never a question of a standard solution.
Resilience A new gasket has impressive resilience, exactly like a young person looking forward to a long life. The gasket expands and fills its groove in order to seal in the media that flow through the exchanger. This is the condition that we want to maintain. But since rubber is an organic material, it is affected by its ambient environment —in other words, it ages. This is unavoidable. But there are ways to prolong the life of rubber. First of all, this calls for investing in the right type of gasket. Since the plates have deep channels, a design such as an O-ring can t be used, as it is best fitted to serve as a plug. Instead, the right gasket has to be capable of compression in order to resist the stresses and forces that the flow of media can generate. Secondly, the right gasket materials must be selected, and this requires comprehensive expertise in applications and materials. Some applications generate less wear, such as
Long lifetime continued
water/water at low temperatures. A gasket in an exchanger with this type of duty can last for many years without leaking. But there are other applications which quickly reveal the quality of a gasket in no uncertain terms. The process industry is one example. In this sector, heat exchangers handle aggressive media such as lye and acids. If the temperature of these media is also high, the stress on the gaskets can be very great.
Some applications require a plate heat exchanger with gaskets. A quality gasket gives higher reliability.
EPDM and nitrile rubber The two most commonly used materials for gaskets are EPDM and nitrile rubber. EPDM is often used in the processing industry and shows impressive resistance to corrosive media. It is also used in heat exchangers where media temperatures are high, as nitrile rubber is sensitive to these. But this does not mean that EPDM is a general solution for difficult applications.
Limitations It s often said that lik e dissolves like , and in many cases this means that EPDM reacts with oil, swells and then cracks. EPDM can thus not be used in applications such as oil platforms. Although these applications involve very high temperatures, nitrile gaskets are used nevertheless, thanks to a specially developed variant of nitrile rubber. This shows that there is no standardized solution when it comes to selecting a gasket, which in turn means that each compound for gasket material also has to be unique. The compounds are developed with reference to the type of media in the heat exchanger and the ambient environment.
Gasket-free? It could be asked why plate heat exchangers with gaskets are used in the first place. There are gasketfree units that can be cleaned easily with CIP (Cleaning-In-Place) systems. A CIP system is connected to the heat exchanger, which is then washed with a cleaning agent that dissolves scale, among other things. In other words, a CIP system enables cleaning without the need to open the heat exchanger.
One reason for choosing plate heat exchangers with gaskets is that specific applications require units that must be opened in order to clean them. They cannot be maintained in acceptable condition with CIP alone, but must be cleaned mechanically because the channels are blocked by materials that are difficult to dissolve, such as sand, clay or various types of salts. It is possible to dislodge these materials with chemicals, but this involves a risk of attacking the plates as well. Another reason is that plate heat exchangers with gaskets are more flexible. They can easily be opened and reconfigured. They have a broad range of applications, and investing in a gasket-free unit is not always necessary, since gasketed exchangers have enough capacity and are also compact. In addition, they are easy to monitor in terms of dirt, scale and blockages.
Gasket data base Selecting the right gasket is not easy. That s why Alfa Laval s gasket specialists have created a data base comprising all available information on rubber and gasket materials. The computerized data base has been created in order to provide customers with information that is as precise as possible. It responds to questions regarding the media in the heat exchanger and the pressure and temperatures to which the gasket will be exposed. The data base then immediately generates recommendations for appropriate gaskets.
Valutech Inc Tel: Avenue, (905) 940-0961 Toronto 101 Milner Avenue, Ontario M1S 4S6 ¥ Edmonton 4727 - 68th Alberta T6N 2N2 70 Esna Park ¥ Drive, 3 299-3535 Fax: (905) Tel.: (416) 299-6101 ¥ Toll Free 1-888-ALFACAN Fax:Unit (416) ¥ 940-0983 www.alfalaval.ca Markham, Ontario, L3R 6E7
E-Mail: [email protected]
Heat Exchangers • Process Equipment • Control Valves • Steam Traps • Mixers • Industrial Valves • Technical Services
Related Documents
Technical Paper
June 2020 5
Generic-technical-paper-skeleton
July 2020 3
Technical Paper Green Buildings
June 2020 9
Technical Paper 2017.docx
June 2020 4