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Heat supply of agglomeration areas
Energy Convers. Mgrnt Vol. 22, pp. 389 to 391, 1982
0196-8904/82/040389-03503.00/0 Copyright ~'~ 1982 Pergamon Press Ltd
Printed in Great Britain. All rights reserved
H E A T S U P P L Y OF A G G L O M E R A T I O N
AREAS
A. D U T Z and R. JANK Kernforschungsanlage Jfilich und peb GmbH, Berlin (Received 16 November 1981)
Abstract--The technologies of heat supply for agglomeration areas will, in the future, undergo appreciable changes compared to the present status. There will be a strong enhancement of the use of domestic energy sources like solid waste, biogas and biomass or coal. Perhaps the strongest momentum will come from efforts to make use of the large potential of industrial waste heat, which is generally in the same order of magnitude as the demand for heating energy. Since we have different temperature levels here compared to conventional district heating, different technologies will be employed, in particular connected with low temperature applications. Some of them are described in the paper, and the main results of an investigation are reported, where the potential of application in an area of about 400,000 inhabitants were studied.
The conventional supply of heat for heating purposes and tap-water preparation is based generally on gas, oil, electricity and district-heating. These systems are at present rather independent from each other, influencing each other only by setting the level of costs of the competing technologies. This situation is undergoing a change at present, caused primarily by the dramatic increases of energy prices during the last few years. Perhaps the most important fact in this respect is the recovery of waste energy from industry: the characteristics of agglomeration areas is a mixture of living areas and industrialized areas, where very often more waste heat is rejected to the surroundings than would be needed for heating and tap-water preparation. As an example, in Germany the industrial reject heat potential is about 40 Mio t SKE, most of which is produced in agglomeration areas; on the other hand, the need for low-grade heat energy in these areas is around 50 Mio t SKE. Therefore, in principle almost all of this demand could be covered by reject heat. In practice, of course, there are many impediments which have in the past prevented a systematic utilization. Among these, costs are the most important, but not the only factor. District-heating with cogeneration can also be considered as waste-heat utilization. Since it allows for appreciable energy savings as well as for a very effective substitution of oil, it is very strongly discussed at present in many countries. It was estimated recently, that in the German case about 30~o of the overall heating demand can be covered by this technology [1]. A consequent increase of this technology--which covers only 7~o at present--has many consequences to the overall structure of energy supply of the whole country. On the one hand, cogeneration substitutes the heat supply with gas and with electricity, which have a much worse energy utilization factor; on the other hand cogeneration also means the production of electricity, thereby partly substituting large power-plants erected at 389
larger distances from the consumers. Because of the different variations for the demand of heat and electricity during the course of the year, it can be expected that there conflicts arise of economic and technical nature between the different suppliers. An increased use of industrial waste heat would help appreciably in weakening the potential of these conflicts. The use of this waste heat is generally combined with substantial organizational problems, since a number of reject heat emitters with seasonally varying output--being additionally dependent from market developments--have to be connected with many thousands of individual customers with different characteristics of demand, the whole system being managed by a third market sector, the suppliers of district heat. This problem is released to some extent, if the waste heat can be used directly for heating purposes. However, generally only steel mills and some chemical industries reject waste heat having a sufficiently high temperature level of 100°C or higher. In these cases, large efforts are made at present in Germany to feed this heat into existing or new district heating systems. But it has to be asked here, if these industries, perhaps with some changes in their technical processes, could produce electricity instead of waste heat, using newly developed ORC turbines which may be utilized economically already at temperatures of 150° 200°C? The major part of the industrial waste heat is rejected at a temperature level of 40°C or below. Therefore, it cannot be used directly for heating purposes but has to be graded up by heat pumps, driven with electricity, diesel or gas. It is this feature, which may help to reduce some of the problems connected with a forced introduction of district heating, since it allows the suppliers of gas and electricity to participate further on the heating market, using many of their installations already taken today but with the advantage of a very much better utilization of their products from the standpoint of energy
390
DUTZ AND JANK: HEAT SUPPLY OF AGGLOMERATION AREAS
saving. As an example, electric heat pumps within a system described above use electricity 5-6 times more efficiently than electric storage heaters. Whereas a consequent use of industrial waste heat in agglomeration areas will lead to huge savings of energy, it requires certain changes in the techniques of heat supply of the individual houses, in the whole energy supply system of the region and in urban and regional planning as well. The most significant change is the transition to low temperature heating systems. In principle, for heating and also for tapwater preparation, temperatures of 60°C are enough. The much higher temperatures used in conventional district heating (up to 140°C) are the result of economic optimizations based on energy costs of the past. Today, even with these systems the optimal inlet temperature would hardly surmount 100°C. On the other hand, systems with heat pumps have a stronger dependence on temperature. The optimal temperature here is in the range of 50°C. But this presupposes that the whole system is optimized: temperature levels, radiator areas and thermal insulation measures of the individual buildings. The low temperature of the waste heat allows for much simpler and cheaper transport pipelines: here, the costs can be 50~o lower than high temperature pipelines. Since the costs for heat distribution make about 60% of the overall costs in district heating, by this low temperature system much larger distances can be covered. This is an advantage of great importance because, instead of the 15-20 km distances of today, one can propose a supply of heat over 50 km or even more. Therefore, the economic potential of these low temperature systems exceeds the potential of conventional district heating, thereby also increasing the possible share of these systems on the heat supply market from the 30~o cited above to some 4 ~ 5 0 ~ . It can hardly be imagined that there is any other measure which may give such effective distributions in solving our present problems in energy supply. The system of low temperature district heating can be realized today without any new developments being necessary. Nevertheless, a number of components can still be improved, in particular the use of the low temperature heat by heat pumps. In this respect there are some very interesting developments under way, e.g. two stage compression heat pumps with absorption cycle promising 30~o better COP's than present heat pumps [2], or heat pump transformers to be used when much more waste heat is available than is needed by the consumers. Here, only the peak demand temperatures are created by the heat pump process, whereas the base load is delivered via the heat transformer process which uses almost no energy at all [3]. Other possible components of the future are thermochemical storage systems, which work also as a special type of heat pump, having the additional possibility of heat storage over long periods almost without any energy losses, a property
which is very strongly desired within such systems. These systems, with comparably high storage densities, re-open the question of whether heat transport by railway may compete with pipe-line technology? Today, this question is open, depending, of course, very strongly on the tariffs offered by the railway administrations. It can be imagined, today, that the supply of smaller living centers with such railway systems may be economically possible even over distances of 40 km and more [2]. A matter of particular relevance is energy storage. Thermal storage suffers from the fact that seasonal storage is totally uneconomic with present means. In that field there is a great deal of research work in some countries, e.g. Sweden, with little immediate success, but with some promising concepts. One of these is aquifer storage--where applicable for geological reasons--which is closely connected with low temperature systems. Aquifer storage offers the possibility of realizing even seasonal storage, at least when working with costless available reject heat. On the contrary, a still more ambitious goal being today without any chance of realization. Another storage facility is electrical night storage, which has become a very familiar heating system in some European countries during the last two decades. However, it has to be asked if these systems provide us with a satisfying energy utilization. For the electricity supplier, the same effect would be achieved by operating heat pumps during times of low load, storing the heat produced with thermal storage. With the exception of air/water heat pumps, very good COP's could be accounted for, thus making use of the same amount of electricity for a much larger demand of heat. On the electrical side, newly developed electrochemical batteries like the Na/S-system may be at hand in the near future, which could remove almost completely the problem of peak load electricity when being operated decentralized in transformer stations, storing electricity during low load and generating electricity during peak load times. By these two systems, the electricity wasting electric storage heaters may perhaps disappear in the medium range again. We have mentioned above a number of new concepts and developments which may prove to be of more or less importance in the heat supply systems of the future. They have to be supplemented by energy sources like solid waste, biogas, gas from sewage water and biomass, which will always be available in larger agglomeration areas. It turns out that energy engineers, communal and regional planners and architects will have to investigate the whole problem of energy supply of agglomeration areas in a much more comprehensive way considering the fact of numerous mutual correlations where until now only individual and independent systems have been regarded. In this area, large changes to the systems can be expected in the forthcoming decades and components will be involved in these systems which may be
DUTZ AND JANK:
HEAT SUPPLY OF AGGLOMERATION AREAS
391
regarded as being rather unconventional from the stand point of today. This transition will also lead to a substantial reduction of energy demand and energy loss, thereby having very positive effects on ecology. Because of the large investments necessary in this field (as an example as much as 400 billion DM will have to be spent by the German electricity suppliers until 2000) decisions will always be influenced not only by pure calculations of economics, but also by political debates which are concerned with more general questions like centralized vs decentralized systems, problems of nuclear energy, systems stability and safety against terroristic activities, independence from other countries and other factors. These discussions will preserve their importance in the years to come. But in the light of the huge investments mentioned above, the basis of this discussion must be economic data. Therefore we will give finally some results of investigations made very recently in connection with a low temperature district heating system which was proposed for the agglomeration area of Ludwigshafen, Germany. In and around the city of Ludwigshafen there are situated the cities of Worms, Frankenthal and Speyer, with more than 400,000 inhabitants altogether. Taking apart smaller or medium sources of waste heat, seven large waste heat emitters remain, namely three different chemical works, two nuclear power plants and a waste ignition plant. Whereas the maximum heat demand in that area is about 2000 MWh, the waste heat sources mentioned deliver 3150 MWh. It can be seen, that even if one considers only the "best" sources of waste heat with regard to their capacity, average temperature and local position, the availability of waste heat exceeds the maximum heat demand appreciably. This seems to be a general feature of industrialized agglomeration areas [4]. The investigation was based on a rather detailed study of the structure in the area and a first optimization of the system, where waste heat of 25-35°C is upgraded to usable temperature by rather decentralized heat pumps. The following main conclusions can be drawn from these comprehensive calculations:
(60-70 DM/MWh), which on the other hand are most frequently structures grown up for decades. Therefore, this comparison is not quite fair. (4) The optimal difference in temperature between outlet and return water in the primary system is between 10 and 20 K. On the contrary, with conventional district heating this would be 70-100 K. The extension of the supply area is about 45 km. The diameter of the main transport lines (for a capacity of 700 MW) is 1500 mm. (5) Presumably no thermal insulation is necessary for the transport pipelines. Temperature losses are in the range of 2-4 K over the whole distance. (6) With electric heat pumps, small units for individual buildings are preferable. Using Diesel/gas heat pumps, larger stations of about 1 MW lead to better economic results than small ones. (7) Since the main investment for the system is for the heat pumps which have to be installed only at the time when the consumers are actually connected, the financial risks are reduced compared to conventional systems, where the main costs have to be paid at the very beginning. (8) Low temperature district heating enhances appreciably the flexibility of energy planning for the whole region. In particular, it may decrease the overall costs by avoiding simultaneous supply in the same region of gas, electric heating and district heating.
(1) Using Diesel or gas driven compression heat pumps, the energy efficiency of the system is as good or even better than present conventional cogeneration (being itself generally not optimized with respect to energy). (2) Using conventional electric heat pumps, the energy efficiency is about 20% worse than with Diesel heat pumps. (3) The specific net costs of heat for the consumer are in the range of 80-90 DM/MWh, thus being higher than average cogeneration costs of today
REFERENCES
Whereas conventional district heating is a very familiar system where all components can readily be optimized in terms of economics, this system as a whole is completely new. Almost all components show a wide variety in specifications and characteristics, allowing for different optimizations. Many technical improvements are still possible, some of them have been mentioned above. This may improve the economics as well. The costs of the system calculated in this study are within a very reasonable magnitude, encouraging to the hope that this system or similar ones will get a chance of realization somewhere in Germany in the near future.
[1] Gesamtstudie Fernwiirme (General District Heating stud),, an investigation of the technical and economic possibilities of this technology in Germany), Bundesministerium ffir Forschung und Technologic (BMFT), Bonn (1977). [2] Stadtwerke Mannheim (H. P. Winkens, U. Mucic et al.), Alternative energy supply for the RheinNeckar area. Study under way with the support of the BMFT. [3] G. Alefeld, in Brennstoff~ Wiirme, KraJt (1981). [4] A. Krebs, R. Jank and P. Steiger, in Proc. First lEA-conference on Energy Conservation Technologies and their Commercialisation, Berlin (1981).
0196-8904/82/040389-03503.00/0 Copyright ~'~ 1982 Pergamon Press Ltd
Printed in Great Britain. All rights reserved
H E A T S U P P L Y OF A G G L O M E R A T I O N
AREAS
A. D U T Z and R. JANK Kernforschungsanlage Jfilich und peb GmbH, Berlin (Received 16 November 1981)
Abstract--The technologies of heat supply for agglomeration areas will, in the future, undergo appreciable changes compared to the present status. There will be a strong enhancement of the use of domestic energy sources like solid waste, biogas and biomass or coal. Perhaps the strongest momentum will come from efforts to make use of the large potential of industrial waste heat, which is generally in the same order of magnitude as the demand for heating energy. Since we have different temperature levels here compared to conventional district heating, different technologies will be employed, in particular connected with low temperature applications. Some of them are described in the paper, and the main results of an investigation are reported, where the potential of application in an area of about 400,000 inhabitants were studied.
The conventional supply of heat for heating purposes and tap-water preparation is based generally on gas, oil, electricity and district-heating. These systems are at present rather independent from each other, influencing each other only by setting the level of costs of the competing technologies. This situation is undergoing a change at present, caused primarily by the dramatic increases of energy prices during the last few years. Perhaps the most important fact in this respect is the recovery of waste energy from industry: the characteristics of agglomeration areas is a mixture of living areas and industrialized areas, where very often more waste heat is rejected to the surroundings than would be needed for heating and tap-water preparation. As an example, in Germany the industrial reject heat potential is about 40 Mio t SKE, most of which is produced in agglomeration areas; on the other hand, the need for low-grade heat energy in these areas is around 50 Mio t SKE. Therefore, in principle almost all of this demand could be covered by reject heat. In practice, of course, there are many impediments which have in the past prevented a systematic utilization. Among these, costs are the most important, but not the only factor. District-heating with cogeneration can also be considered as waste-heat utilization. Since it allows for appreciable energy savings as well as for a very effective substitution of oil, it is very strongly discussed at present in many countries. It was estimated recently, that in the German case about 30~o of the overall heating demand can be covered by this technology [1]. A consequent increase of this technology--which covers only 7~o at present--has many consequences to the overall structure of energy supply of the whole country. On the one hand, cogeneration substitutes the heat supply with gas and with electricity, which have a much worse energy utilization factor; on the other hand cogeneration also means the production of electricity, thereby partly substituting large power-plants erected at 389
larger distances from the consumers. Because of the different variations for the demand of heat and electricity during the course of the year, it can be expected that there conflicts arise of economic and technical nature between the different suppliers. An increased use of industrial waste heat would help appreciably in weakening the potential of these conflicts. The use of this waste heat is generally combined with substantial organizational problems, since a number of reject heat emitters with seasonally varying output--being additionally dependent from market developments--have to be connected with many thousands of individual customers with different characteristics of demand, the whole system being managed by a third market sector, the suppliers of district heat. This problem is released to some extent, if the waste heat can be used directly for heating purposes. However, generally only steel mills and some chemical industries reject waste heat having a sufficiently high temperature level of 100°C or higher. In these cases, large efforts are made at present in Germany to feed this heat into existing or new district heating systems. But it has to be asked here, if these industries, perhaps with some changes in their technical processes, could produce electricity instead of waste heat, using newly developed ORC turbines which may be utilized economically already at temperatures of 150° 200°C? The major part of the industrial waste heat is rejected at a temperature level of 40°C or below. Therefore, it cannot be used directly for heating purposes but has to be graded up by heat pumps, driven with electricity, diesel or gas. It is this feature, which may help to reduce some of the problems connected with a forced introduction of district heating, since it allows the suppliers of gas and electricity to participate further on the heating market, using many of their installations already taken today but with the advantage of a very much better utilization of their products from the standpoint of energy
390
DUTZ AND JANK: HEAT SUPPLY OF AGGLOMERATION AREAS
saving. As an example, electric heat pumps within a system described above use electricity 5-6 times more efficiently than electric storage heaters. Whereas a consequent use of industrial waste heat in agglomeration areas will lead to huge savings of energy, it requires certain changes in the techniques of heat supply of the individual houses, in the whole energy supply system of the region and in urban and regional planning as well. The most significant change is the transition to low temperature heating systems. In principle, for heating and also for tapwater preparation, temperatures of 60°C are enough. The much higher temperatures used in conventional district heating (up to 140°C) are the result of economic optimizations based on energy costs of the past. Today, even with these systems the optimal inlet temperature would hardly surmount 100°C. On the other hand, systems with heat pumps have a stronger dependence on temperature. The optimal temperature here is in the range of 50°C. But this presupposes that the whole system is optimized: temperature levels, radiator areas and thermal insulation measures of the individual buildings. The low temperature of the waste heat allows for much simpler and cheaper transport pipelines: here, the costs can be 50~o lower than high temperature pipelines. Since the costs for heat distribution make about 60% of the overall costs in district heating, by this low temperature system much larger distances can be covered. This is an advantage of great importance because, instead of the 15-20 km distances of today, one can propose a supply of heat over 50 km or even more. Therefore, the economic potential of these low temperature systems exceeds the potential of conventional district heating, thereby also increasing the possible share of these systems on the heat supply market from the 30~o cited above to some 4 ~ 5 0 ~ . It can hardly be imagined that there is any other measure which may give such effective distributions in solving our present problems in energy supply. The system of low temperature district heating can be realized today without any new developments being necessary. Nevertheless, a number of components can still be improved, in particular the use of the low temperature heat by heat pumps. In this respect there are some very interesting developments under way, e.g. two stage compression heat pumps with absorption cycle promising 30~o better COP's than present heat pumps [2], or heat pump transformers to be used when much more waste heat is available than is needed by the consumers. Here, only the peak demand temperatures are created by the heat pump process, whereas the base load is delivered via the heat transformer process which uses almost no energy at all [3]. Other possible components of the future are thermochemical storage systems, which work also as a special type of heat pump, having the additional possibility of heat storage over long periods almost without any energy losses, a property
which is very strongly desired within such systems. These systems, with comparably high storage densities, re-open the question of whether heat transport by railway may compete with pipe-line technology? Today, this question is open, depending, of course, very strongly on the tariffs offered by the railway administrations. It can be imagined, today, that the supply of smaller living centers with such railway systems may be economically possible even over distances of 40 km and more [2]. A matter of particular relevance is energy storage. Thermal storage suffers from the fact that seasonal storage is totally uneconomic with present means. In that field there is a great deal of research work in some countries, e.g. Sweden, with little immediate success, but with some promising concepts. One of these is aquifer storage--where applicable for geological reasons--which is closely connected with low temperature systems. Aquifer storage offers the possibility of realizing even seasonal storage, at least when working with costless available reject heat. On the contrary, a still more ambitious goal being today without any chance of realization. Another storage facility is electrical night storage, which has become a very familiar heating system in some European countries during the last two decades. However, it has to be asked if these systems provide us with a satisfying energy utilization. For the electricity supplier, the same effect would be achieved by operating heat pumps during times of low load, storing the heat produced with thermal storage. With the exception of air/water heat pumps, very good COP's could be accounted for, thus making use of the same amount of electricity for a much larger demand of heat. On the electrical side, newly developed electrochemical batteries like the Na/S-system may be at hand in the near future, which could remove almost completely the problem of peak load electricity when being operated decentralized in transformer stations, storing electricity during low load and generating electricity during peak load times. By these two systems, the electricity wasting electric storage heaters may perhaps disappear in the medium range again. We have mentioned above a number of new concepts and developments which may prove to be of more or less importance in the heat supply systems of the future. They have to be supplemented by energy sources like solid waste, biogas, gas from sewage water and biomass, which will always be available in larger agglomeration areas. It turns out that energy engineers, communal and regional planners and architects will have to investigate the whole problem of energy supply of agglomeration areas in a much more comprehensive way considering the fact of numerous mutual correlations where until now only individual and independent systems have been regarded. In this area, large changes to the systems can be expected in the forthcoming decades and components will be involved in these systems which may be
DUTZ AND JANK:
HEAT SUPPLY OF AGGLOMERATION AREAS
391
regarded as being rather unconventional from the stand point of today. This transition will also lead to a substantial reduction of energy demand and energy loss, thereby having very positive effects on ecology. Because of the large investments necessary in this field (as an example as much as 400 billion DM will have to be spent by the German electricity suppliers until 2000) decisions will always be influenced not only by pure calculations of economics, but also by political debates which are concerned with more general questions like centralized vs decentralized systems, problems of nuclear energy, systems stability and safety against terroristic activities, independence from other countries and other factors. These discussions will preserve their importance in the years to come. But in the light of the huge investments mentioned above, the basis of this discussion must be economic data. Therefore we will give finally some results of investigations made very recently in connection with a low temperature district heating system which was proposed for the agglomeration area of Ludwigshafen, Germany. In and around the city of Ludwigshafen there are situated the cities of Worms, Frankenthal and Speyer, with more than 400,000 inhabitants altogether. Taking apart smaller or medium sources of waste heat, seven large waste heat emitters remain, namely three different chemical works, two nuclear power plants and a waste ignition plant. Whereas the maximum heat demand in that area is about 2000 MWh, the waste heat sources mentioned deliver 3150 MWh. It can be seen, that even if one considers only the "best" sources of waste heat with regard to their capacity, average temperature and local position, the availability of waste heat exceeds the maximum heat demand appreciably. This seems to be a general feature of industrialized agglomeration areas [4]. The investigation was based on a rather detailed study of the structure in the area and a first optimization of the system, where waste heat of 25-35°C is upgraded to usable temperature by rather decentralized heat pumps. The following main conclusions can be drawn from these comprehensive calculations:
(60-70 DM/MWh), which on the other hand are most frequently structures grown up for decades. Therefore, this comparison is not quite fair. (4) The optimal difference in temperature between outlet and return water in the primary system is between 10 and 20 K. On the contrary, with conventional district heating this would be 70-100 K. The extension of the supply area is about 45 km. The diameter of the main transport lines (for a capacity of 700 MW) is 1500 mm. (5) Presumably no thermal insulation is necessary for the transport pipelines. Temperature losses are in the range of 2-4 K over the whole distance. (6) With electric heat pumps, small units for individual buildings are preferable. Using Diesel/gas heat pumps, larger stations of about 1 MW lead to better economic results than small ones. (7) Since the main investment for the system is for the heat pumps which have to be installed only at the time when the consumers are actually connected, the financial risks are reduced compared to conventional systems, where the main costs have to be paid at the very beginning. (8) Low temperature district heating enhances appreciably the flexibility of energy planning for the whole region. In particular, it may decrease the overall costs by avoiding simultaneous supply in the same region of gas, electric heating and district heating.
(1) Using Diesel or gas driven compression heat pumps, the energy efficiency of the system is as good or even better than present conventional cogeneration (being itself generally not optimized with respect to energy). (2) Using conventional electric heat pumps, the energy efficiency is about 20% worse than with Diesel heat pumps. (3) The specific net costs of heat for the consumer are in the range of 80-90 DM/MWh, thus being higher than average cogeneration costs of today
REFERENCES
Whereas conventional district heating is a very familiar system where all components can readily be optimized in terms of economics, this system as a whole is completely new. Almost all components show a wide variety in specifications and characteristics, allowing for different optimizations. Many technical improvements are still possible, some of them have been mentioned above. This may improve the economics as well. The costs of the system calculated in this study are within a very reasonable magnitude, encouraging to the hope that this system or similar ones will get a chance of realization somewhere in Germany in the near future.
[1] Gesamtstudie Fernwiirme (General District Heating stud),, an investigation of the technical and economic possibilities of this technology in Germany), Bundesministerium ffir Forschung und Technologic (BMFT), Bonn (1977). [2] Stadtwerke Mannheim (H. P. Winkens, U. Mucic et al.), Alternative energy supply for the RheinNeckar area. Study under way with the support of the BMFT. [3] G. Alefeld, in Brennstoff~ Wiirme, KraJt (1981). [4] A. Krebs, R. Jank and P. Steiger, in Proc. First lEA-conference on Energy Conservation Technologies and their Commercialisation, Berlin (1981).