Solution approaches for energy optimization in the water sector Michael Reinders, 1 Sylvia Gredigk-Hoffmann, 1 Dr. Henry Risse, 1 Maja Lange, 1

Transcription

1 Solution approaches for optimization in the water sector Michael Reinders, 1 Sylvia Gredigk-Hoffmann, 1 Dr. Henry Risse, 1 Maja Lange, 1 1 Research Institute for Water and Waste Management (FiW) at the RWTH Aachen University e.v., Aachen, North Rhine-Westphalia, Germany Abstract Energy-saving and environment-friendly generation gain more and more importance in social perception. Even the water sector has potential to support these efforts. Wastewater treatment plants (WWTP) for example are highly -consuming. Nowadays their demand is mostly covered by fossil sources. However WWTP are suitable as location for the generation of renewable. Digester gas or biogas is a renewable source, which is produced mainly on major WWTP. The EuWaK project tests a pilot plant to produce biomethane and hydrogen out of biogas and utilize the products as vehicle fuel (biomethane) and source (hydrogen) to generate electrical and heat for a nearby school. A concept for the integration of hydrogen production and utilization at WWTP is illustrated using the example of the EuWaK project. Keywords: Energy, EuWaK, optimization, biomethane, hydrogen Introduction During the last years results of research indicate a change of the power generation and supply. Based on aspects of climate and environment protection and limitedness of fossil sources a conversion of the supply is required using renewable or alternative sources. Besides the implementation of new supply solutions, which address climate and environmental issues, the identification of conservation and improved efficiency are fields of on-going research and development activities. The water sector consumes a lot of. In urban areas wastewater treatment plants (WWTP) are classified as mayor consumers. In Germany WWTP needed approx. 4,400 GWh of electric (Haberkern et al. 2008). Regarding the prices the consumption becomes more and more an important economic aspect for consumers. Since 2002 the price for electric has increased about 60 % in Germany (VIK price index January 2012), whereby the peak is not yet reached. Besides an economical perspective an environmental perspective of the situation changes the future of the sector which is affecting the water sector as well. The conservation of natural resources and the environment will be given priority to. The use of renewable sources and -saving technologies are part of a future strategy in order to achieve the aim of environment-friendly power generation and consumption. The water sector offers a high potential for electrical and thermal self-supply. Especially WWTP provide a great potential for the generation of renewable. But a low usage has not the highest priority in the water sector. The waste water treatment s ultimate objective is the protection of all water bodies influenced by waste water. Low consumption is a secondary aim which is developed with regard to the climate change, resource depletion and the possible consequences of nuclear power accidents. Page 1 of 8

2 At WWTP digester gas (biogas), which is produced during the anaerobic sewage sludge stabilisation, is used as renewable source. Large WWTP use digester gas in combined heat and power plants (CHP) for on-site power generation. An enhanced digester gas production is possible using Co-fermentation, co-treatment of organic substances or wastes in the fermentation unit, at WWTP. Alongside the digester gas usage wind converters, photovoltaic units or small hydropower plants are used. WWTP turn into sites for the generation of renewable for self supply. This is one step on the way towards self-sufficient WWTP. Furthermore, new usage applications of digester gas are investigated, like the processing into biomethane and hydrogen. WWTP reveal potential to produce renewable as element of decentralized supply systems. Different approaches for the electricity consumption of WWTPs and the usage of digester gas (biogas) are available. Heat potentials, an adapted heat production or heat storage, digester gas processing into for example biomethane are possibilities for supply at WWTP (Risse et al. 2011). The EuWaK-Project 1 at the WWTP Bottrop (Operator: Emschergenossenschaft), North Rhine-Westphalia, Germany, is a pilot project in order to test and develop the processing of digester gas into biomethane and hydrogen. Project partners are Tuttahs & Meyer ltd. (T&M), the Redlich and Partner GmbH (IBR), the city of Bottrop and the Research Institute for Water and Waste Management at the RWTH Aachen University (FiW) (Teichgräber et al. 2010). Worldwide the process concept of the pilot plant and the integration into the wastewater treatment process are realised for the first time. Figure 1 shows the locations of the pilot plant units on a local map (top figure) and at the WWTP Bottrop (lower figure). 2 Container BGA and HCG H2 pipeline and H2 CHP Filling station WWTP Bottrop WWTP also provide potential for a future hydrogen infrastructure. As decentralized location WWTP can be part of a decentralized hydrogen infrastructure. The generation of digester gas as reactant for the production of hydrogen, the capacity of qualified personal and a public supply is given. These exemplary aspects qualify WWTP as location for the on-site production of hydrogen. On the way to selfsupply WWTP can participate in climate protection using renewable sources to reduce CO 2 emissions (Gredigk-Hoffmann et al. 2004). Page 2 of 8 Tankstelle filling station Gasaufbereitung BGA and HCG units H2 GH pipeline 2 -Leitung to H2 CHP zumat BHKW Welheimer Mark Mark Figure 1: Locations of the pilot plant units at WWTP Bottrop, Germany (Source: Emschergenossenschaft/ bte - Beratungsteam Energie und Verfahrenstechnik) 1 EuWaK Project: Erdgas und Wasserstoff aus Kläranlagen Natural gas and hydrogen at WWTP

3 The produced biomethane is mostly used as reactant for the processing into highly pure hydrogen. A smaller amount is discharged to a filling station, where natural gas vehicles are fuelled. The system illustrates the processing of sewage sludge into hydrogen using the intermediate steps digester gas and biomethane. A school is the end-consumer for the produced and heat of the hydrogen combined heat and power plant (H 2 CHP). In the following the EuWaK project is explained as example for a possibility of optimization in the water sector. Methods The EuWaK project demonstrates the processing of digester gas into biomethane and further into hydrogen. The processes, cleaning and processing of biogas to biomethane (BGA), transforming biomethane into hydrogen (HCG), the biomethane filling station and the H 2 CHP, are independent units. The BGA is connected to the HCG process and the filling station. The HCG process supplies the H 2 CHP with highly pure hydrogen. The BGA process contains the steps biogas compression, gas conditioning, methane enrichment and transfer of the product gas. The HCG process is divided into reverse osmosis, steam reforming, cooling, hydrogen enrichment, pressure boosting and storage and transfer of the product gas (see figure 2). At the WWTP Bottrop a H 2 filling station is located. It is operated by Emschergenossenschaft. For the future a supply of the filling station by the EuWaK pilot plant is planed (see figure 2). Figure 2: Process pattern EuWaK unit (Source: Emschergenossenschaft/ bte - Beratungsteam Energie und Verfahrenstechnik) In Figure 2 the operating procedure of the entire EuWaK process is illustrated. An alternative option for the biomethane filling station is the discharge of biomethane into the natural gas grid observing its regulations (see figure 2). Table 1: Parameter EuWaK pilot plant (Source: Emschergenossenschaft/ bte - Beratungsteam Energie und Verfahrenstechnik) Parameter Value Unit Input Digester gas/ biogas 120 m³ biogas/ h Output PSA (Biomethane) 72 m³ CH 4 /h Input HCG m³ CH 4 /h Output hydrogen for H 2 CHP m³ H 2 /h Output biomethane for filling station m³ CH 4 /h Table 1 summarises the input and output volumes of BGA and HCG, which are outlined in the following. At the BGA 120 m³ biogas/h is processed into m³ biomethane/h depending on the methane concentration of the biogas. A part of the digester gas, produced during the anaerobic sludge treatment, enters the BGA and is compressed from atmospheric pressure to approx. 600 kpa. The compression is followed by several gas cleaning units. The gas flows through a twostage activated carbon filter to reduce the hydrocarbon - hydrocarbons which are not methane (CH 4 ) - concentration. A desulphurization decreases the hydrogen Page 3 of 8

4 sulphide (H 2 S) and siloxane concentration. A hydrogen sulphide concentration of < 5,0 mg/m³ must be observed. Using heat exchanger water and any volatile substances, which condense at temperature up to 3 to 5 C, condense during the process. These substances are derived from the process. The biogas is heated up to about 20 C and flows through a prefilter into a pressure swing adsorption (PSA). Inside the PSA carbon dioxide (CO 2 ) is separated from CH 4. The methane-rich gas is product gas and CO 2 - rich gas streams back into the digester gas storage tank. The product gas (biomethane) is used as reactant for the production of hydrogen. A smaller amount is used in a car filling station by the Emschergenossenschaft. The filling station offers a storage place of 460 m³ at a pressure of kpa. At the HCG m³ biomethane/h is processed into m³ H 2 /h. The biomethane enters the HCG after the BGA process where it is divided into feed gas and fuel gas. The fuel gas feeds a FLOX burner, a flameless oxidation process. The FLOX -burner, integrated into the reformer unit, supplies the reformer with heat to reach and keep the operating temperature. The feed gas is one reactant of the steam reforming and enters the reformer after a compression to approx kpa. The necessary steam is produced inside the reformer by vaporisation of purified water. A reverse osmosis is used to produce the purified water. Inside the reformer biomethane and steam react with a nickel catalyst mainly to hydrogen (H 2 ), carbon dioxide, carbon monoxide (CO), steam, inert substances in BGA product gas, like nitrogen, and hydrocarbons which are not transformed at a temperature of ca. 900 C. Downstream the reformer a CO-Shift, temperature of approx. 350 C, is situated. Most carbon monoxide reacts at 350 C and with an iron chromium catalyst to CO 2 and steam. Using PSA the H 2 concentration increases. The PSA product is highly pure hydrogen. The CO 2 -rich gas is a by-product of PSA and serves as fuel gas for the FLOX -burner whereby the amount of biomethane as fuel gas is lowered. The highly pure H 2 flows through a pipeline to a hydrogen combined heat and power plant (H 2 CHP) which is located at a nearby school (Welheimer Mark). The H 2 CHP has an electrical power capacity up to 70 kw. The power and heat is consumed for the heating and the use of the school buildings. Results The research and development project EuWaK is implemented during a start-up phase (Phase I), April 2005 to December 2008, and an explorative phase (Phase II) from December 2009 until June Worldwide the EuWaK process concept of the pilot plant and its integration into the wastewater treatment process are realized for the first time. The contents of the start-up phase were the planning and authorization, the construction, the start-up and the optimization of the pilot plant. The planning, the construction and the authorization of the pilot plant demanded pioneering and development by communicating with manufacturers and public bodies. Some technologies, like the H 2 CHP, or their interconnection were not available and established. Innovative technical solutions were developed in communication with manufacturers in order to combine the single processes to a total system (Phase I). The fundamentals for a reliable and secure operating were nailed. Optimization measures were realized at technical processes and their control as well as at the Page 4 of 8

5 total system. The successful completion of phase I allowed the start of phase II. The explorative phase is still on-going. The second project phase aims to research and to optimize the process concept, the process control and the interconnection of single processes. Both project phases enable access to scientific evidence which is and will be useful for the specialist community, especially regarding the interconnection of the single processes to a total system. An optimization measure, implemented during phase I, is the development and construction of an additional activated carbon filter system. The installed cleaning system was constructed based on analysis of the WWTP digester gas. In order to reduce minor components of the digester gas an activated carbon filter is taken in operation to secure the pilot plant against for example industrial incidents. These incidents can influence the biogas composition. Minor components, which do not appear daily, can occur in individual cases. Furthermore an online analyser, a process gas chromatograph, is installed to detect the breakdown of the activated carbon bed. A second activated carbon filter is downstream to ensure the continuous operating of the system. The operating of the pilot plant is paused for maintenance work and optimization measures during phase II. Individual runs demonstrated potential of optimization to increase the level of efficiency of single components and the total system. The optimization potential is transferred into measures. Running modifications make an impact and increase the efficiency. Single complexities of the interconnections only occur after extended operating hours. The BGA runs without major modifications. If the HCG stops, the BGA will only feed the storage tank of the filling station. The HCG operation is only paused due to optimization measures in order to improve its performance. The filling station depends on the BGA operation and the storage tank s filling level. The H 2 CHP is supplied by the HCG through a pipeline. The H 2 pipeline can store a small amount of H 2. It must be filled all the time to prevent infiltration of contaminants. The EuWaK pilot plant is designed for a continuous operation, wherefore a storage tank is not integrated into the system. In 2011 the BGA unit produced biomethane with a methane concentration not lower than 95,5 Vol.-%. The methane concentration fluctuates between 95,5 Vol.-% and above 99 Vol.-% in By now the BGA can reach a total level of efficiency (energetic) of approx. 80 %. The quality of the biomethane is continuous, which is important for the processing of biomethane into hydrogen. The HCG unit needs an input methane concentration of 96 Vol.-% in the produced biomethane. The BGA s product gas is returned to the PSA process (BGA) until the required methane concentration is reached. A small amount of the methane concentration is recovered in the by-product of the PSA (BGA). The biogas of the WWTP Bottrop consists of 60 to 65 Vol.-% methane and 35 to 40 Vol.-% carbon dioxide. Approximately the percentage of methane generates the output volume of biomethane relating to the input volume. The methane in the by-product of the PSA (BGA) does not get lost for the process or is delivered into the environment, because the by-product is fed into the WWTP biogas storage tank. Thereby the CO 2 concentration in the biogas rises and the methane Page 5 of 8

6 concentration decreases why the biogas methane concentration can be lower compared to other WWTP. The proceeding does not affect the performance of the pilot plant or the combined heat and power plants at the WWTP. The filling station is mainly working all year round. More than 15 cars of the Emschergenossenschaft are fueled at the filling station. A raise of cars using the fueling station would be possible, but the biomethane is used mainly to feed the HCG. In 10 month (2011) the total discharge of biomethane amounts to approx kg upon about 615 fueling processes. The operation and control of the HCG unit requires a higher attention during the project. Compared to the BGA the HCG includes even more complex technologies. Especially the interconnection of the reformer with connected processes demands a far-reaching observation. The influences and performance of each process combined in a total system revealed during the research and development project. The project results execute scientific findings which are useful for planed and on-going research projects in this field of research. Especially the interconnections between the single processes clarify the requirements of the different technologies to produce and supply hydrogen. The HCG can reach a total level of efficiency (energetic) of approx. 55 % till now. Shorter operating phases show a lower level of efficiency. The product gas, which is produced during the HCG process, should contain more than 99,999 Vol.-% H 2. It should be pentavalent hydrogen. A H 2 CHP does not need this gas quality. But the pilot plant was designed to supply fuel cells, which in most cases requires an input gas quality of pentavalent hydrogen (specification of the manufacturer). The high input quality is a specification to minimize the risk of malfunction. The choice of a H 2 CHP was based on CHP lesser vulnerability to failures and not only on the economic differences between fuel cell and H 2 CHP. The project s priority was and is the implementation of a steady system to produce biomethane and hydrogen on WWTP in interconnection with the wastewater treatment process. The quality of the H 2 is part of on-going research work. Further components of the product gas, like CO 2 or nitrogen, could be analyzed in order to determine the H 2 concentration. The determination of high H 2 concentrations is difficult. An analysis of exclusion based on minor components of the highly pure hydrogen is planned to determine the H 2 concentration. The production is a linear process, which depends on the operation of the HCG. The pilot phase does not reveal any malfunctions or variation in the CHP s performance.the H 2 CHP reaches a total level of efficiency (energetic) above 30 %. Conditioned by the operation breaks and the maintenance work the efficiency does not reach a higher level while it should be possible. Discussion and Conclusion The EuWaK project is the first project of this type worldwide. It contributes to an increase of knowledge in the field of hydrogen generation out of renewable sources. The planning and authorization, the construction and the technical implementation of the pilot plant into the wastewater treatment process have been a huge challenge which is mastered on the WWTP Bottrop. Also the Page 6 of 8

7 further development of the total system is approached. The explorative phase of EuWaK demonstrates optimization potential at the pilot plant, especially at the HCG. The identified optimization measures are implemented or components of on-going research and development work. The aim is a failure free, continuous operation of the pilot plant all year round only paused by maintenance work. Thereby the level of efficiency of the components and the pilot plant will increase. The continuous explorative phases prove the possible increase of the efficiency. The results reveal higher levels of efficiency for all components of the pilot plant. The utilisation of a fuel cell can increase the pilot plant s total electrical level of efficiency because its level of efficiency is higher compared to a H 2 CHP. The results of a planned analysis phase will prove the quality of the produced highly pure H 2. Besides the level of efficiency the product quality is an important aspect to evaluate the total system. The biogas composition influences the required gas cleaning technologies. Phase I reveals the influence of industrial discharge, especially industrial incidents, on biogas composition. An upgrade of the gas cleaning technology was necessary because of the consequences of an industrial incident on the digester gas composition and the pilot plant. Alternatives for the used technologies at the BGA unit are state of the art. Amine gas treating is a chemical treatment. The methane slip is lower compared to PSA. Another physical treatment is the water scrubbing. All technologies have advantages and disadvantages, which must be balanced by the operator. Pressure water scrubbing or other technologies followed by reforming of biogas are an alternative for the total system. The intermediate step, the proceeding of biomethane, will be no longer necessary if these technologies are used. The H 2 CHP can be replaced by a fuel cell. But presently fuel cells lifetimes are short and their sensitivity towards contaminants is higher compared to a H 2 CHP. Due to the higher price of fuel cells an exchange of a fuel cell would not have been economical and reasonable in case of an irreparable malfunction. The installed technologies are partly compared theoretically with alternative technologies during the project. First studies clarify that alternative technologies might not be realized in semi-industrial or industrial scales like the EuWaK project s components. Aims of on-going research projects are to investigate, develop and identify the potentials of optimization in the water sector. One part of this research and development work is the EuWaK project. The project s aims are to identify the systems and single components requirements to establish the total system on WWTP. Detailed relations between the biogas composition, the processing technologies, the process control and the pilot plant s efficiency are investigated during on-going research work. The technical integration of the pilot plant into the concept of a WWTP is examined based on the results of the operational phase. Figure 3 sketches a possible concept for WWTP with biomethane and hydrogen production as components of a decentralized hydrogen infrastructure. An innovative decentralized infrastructure integrating a WWTP can contribute towards an environment-friendly future. H 2 is a renewable and carbon-neutral Page 7 of 8

8 source. WWTP present synergetic effects (see Figure 3) which can build the basis for the implementation of an innovative concept. The usage of electrolysis, as an example, allows utilization of pure oxygen for aerobic biological treatment units at WWTP. Primarily this kind of concept can decrease the consumption of a WWTP. biogas Decentralized biomethane grid BGA biomethane filling station CHP electric heat biomethane O2 H2 HCG electrolysis WWTP H2-Gas renewable heat H2 Chemical industry Decentralized H2 grid H2- CHP Fuel cell Figure 3: Concept WWTP as part of an H 2 infrastructure WWTP operators can take a step forward towards an -self-sufficient unit. The concept should be part of an innovative modular system. The system s priorities should be to serve climate protection and water pollution control (Gredigk-Hoffmann et al. 2004). Moreover the water supply and wastewater infrastructure offer potential for heat extraction and possibilities for improved efficiency. One aspect is the use of wastewater s thermal. Heat, recovered from wastewater, is a secure and renewable source. The -saving and environment-friendly future started already. The past and present research and development work accompanied by realizations confirms this development. Electric heat References VIK Verband der Industriellen Energie- und Kraftwirtschaft e.v. (2012). VIK- Strompreisindex Mittelspannung (VIK electricity price index - medium voltage). Gredigk-Hoffmann, S.; Bolle, F.-W.; Schröder, M.; Illing, F. (2004): Sewage Treatment plants with Energy Autarky as Component of the Future Hydrogen Infrastructure. International Hydrogen Congress HYFORUM 2004, Clean Energies for the 21 st Century Towards Sustainable Fuels and Hydrogen Industries, Beijing, People s Republic of China, May 2004 Haberkern B., Maier W., Schneider U. (2008) Steigerung der Energieeffizienz auf kommunalen Kläranlagen (Enhanced efficiency in waste water treatment plants). im Auftrag des Umweltbundesamtes (by order oft he Federal Environment Agency - Germany) Risse, H.; Reinders, M.; Wöffen, B.; Schröder M. (2011): Sewage purification plants as a component of decentralized systems. 6 th International Renewable Energy Storage Conference and Exhibition (IRES 2011), Berlin Teichgräber B., Kraft A., Rossol D., Schröder M. (2010). Green Hydrogen and Natural Gas from Digester Gas of Wastewater Treatment Plants. Proceedings of the 18 th World Hydrogen Energy Conference 2010 (WHEC 2010), May Essen, Germany Acknowledgments EuWaK is funded by the federal land of North-Rhine-Westphalia and the European Union. Disclosures The authors have nothing to disclose. Page 8 of 8