Project title: Flexible 75 kwel Stirling CHP-plant for bio-fuels with low emissions and a high fuel utilization

Transcription

1 PSO F&U Project title: Flexible 75 kwel Stirling CHP-plant for bio-fuels with low emissions and a high fuel utilization Stirling Danmark ApS Diplomvej, Building Lyngby Denmark CVR no.: T: F: info@stirling.dk

2 Summary The objective of the project Flexible 75 kwel Stirling CHP-plant for bio-fuels with low emissions and a high fuel utilization was to combine the Danish experiences with the Stirling engine and updraft gasification with the application of the FLOX gas burner technology for developing and demonstrating a flexible biomass-based small scale CHP plant with 75 kw electrical output, high power efficiency and low emissions. Further, the project has aimed at increasing the technology s reliability and decreasing the need for service. Also, the project has included the development of a control and communication system for unmanned start-up and operation of the plant. During the project the objective was altered and so the development of a new Stirling engine design was done on the 4-cylindred 35 kwe Stirling engine instead of the 8-cylindred 75 kwe Stirling engine. Focus has been on designing a more durable engine designed for easy and fast service. Cold test of the engine has been successful and now full-scale hot tests are to be performed. In the project Stirling DK has also in cooperation with project partner Danish Gas Technology Centre developed the Stirling Engine with Diluted Oxidation (SEDIOX) concept which is a combustion technology based on the diluted oxidation principle. A trademark is obtained and also a patent application is filed and pending regarding the SEDIOX combustion chamber concept. All components for the Stirling gasification plant were produced and installed at Svanholm Estate. The plant consisted of one conventional combustion chamber and one SD3E-type Stirling engine. The plant was commissioned in June 2009 and 1,472 hours of operation and 43 MWh of electricity production was achieved before the plant was de-commissioned in February 2010 due to divergences between Svanholm Estate and Stirling DK. During operation the control system including remote access was tested thoroughly and with great success. The new overall control principle for multiple unit operation regarding the control of the flue gas valves and exhaust gas blower is applied on Stirling plants build after this plant. Further, the remote access is also applied on all new plants. The test operation showed issues with the engine interface on the combustion chamber as the heat transfer from the hot flue gas to the engine needs optimisation. Stirling DK has since the identification of this issue developed different solutions to this which has lead to change of the geometry of the engine interface and improved heat transfer to the heater panel of the engine. All in all, the project enabled the production, installation and test operation of the Stirling plant that has formed the basis of the Stirling plants produced and sold by Stirling DK currently and further, the identification of two critical long-term R&D projects (development of the SD4F engine and the SEDIOX concept) to which Stirling DK has great expectations. Page 1 of 21

3 Index 1 Introduction 4 2 Objectives 4 3 Research and development activities Gasifier Modelling Design Combustion chamber and burner - SEDIOX Burner Combustion chamber Re-design of Stirling engine development of SD4F engine Control system Control strategy Remote control and surveillance 14 4 Production of components and installation of plant Production of components Plant host Installation and commissioning of plant 18 5 Test operation Gasifier Stop-and-go operation Relation between temperature of wood gas and tar deposits in wood gas pipes Ash discharge system Combustion chambers and engines Engine interface Control system 20 6 Trademark registration and patent application 20 7 Conclusion 21 Page 2 of 21

4 Appendices Appendix A: Modelling of up-stream gasifier (only available in Danish) Appendix B: SEDIOX combustion chamber (confidential) Appendix C1: Status på FLO beregning af fyrrum til stirlingmotor (only available in Danish) Appendix C2: Status på FLO beregning af fyrrum og pyramidestub til stirlingmotor (only available in Danish) Appendix D: Conventional combustion chamber (only available in Danish) Appendix E: Development of SD4F engine (confidential) Appendix F: Control diagram for multiple units Appendix G: Contract between Svanholm Estate and Stirling DK Appendix H: Plant layout Appendix I: Process diagram final design Appendix J: Registered trademark, SEDIOX (confidential) Appendix K: Letter from Budde Schou - confirming on patent application from Stirling DK (confidential) Figure index Figure 1: New setup for plant outline Figure 2: Section view of gasifier Figure 3: Section view of SEDIOX burner Figure 4: SD4F engine prepared for a cold test Figure 5: Detail from appendix F - control diagram. Control loop for wood gas and combustion air valves Figure 6: Detail from appendix F control diagram. Control loop for the engine load control Figure 7: Detail from appendix F control diagram. Control loop for exhaust gas blower control Figure 8: Screen shot from HMI. Part of control system showing wood chips supply system, gasifier and ash handling system Figure 9: Screen shot from HMI. Part of control system showing combustion chamber and Stirling engine Figure 10: Screen shot from HMI. Part of control system showing water system Page 3 of 21

5 1 Introduction This report marks the conclusion of the project Flexible 75 kwel Stirling CHP-plant for bio-fuels with low emissions and a high fuel utilization funded by Energinet.dk. The project was initiated with the signing of the contract between Energinet.dk and the project partners 30 th of June The project was launched in order to build on the Danish experiences regarding the Stirling engine technology in combination with updraft gasification and diluted oxidation combustion for small scale biomass fuelled CHP applications. The prospects of this combination are very promising in order to achieve low emissions, high operational reliability and low operational costs. Project coordinator is Stirling DK Aps which is the world leading provider of biomass fuelled Stirling engines. The project partners are: The Danish Technical University (DTU) Danstoker A/S The Danish Gas Technology Centre (DGC) TEISLEV energy. Note regarding DTU contribution The work performed by DTU related to this project is done by Jonas Kabell Bovin (JKB). This work is related to the engine development and was done in close cooperation with Stirling DK and so it is not possible to separate the work done by DTU from the work done by DTU. Thus, DTU is not particularly mentioned regarding performed work in this report. However, the work performed by JKB and thereby DTU has been highly valued by Stirling DK and the contribution from DTU has been of great importance for the project. JKB was part time employed by Stirling DK in the last six months of Further, in the fall of 2008 JKB was hired as a full time employee at Stirling DK where he since has been a key R&D specialist regarding the further development of the Stirling engine. 2 Objectives In the application the objective of the project was described as following: The objective of the project is to combine the Danish experiences with the Stirling engine and updraft gasification with the application of the FLOX gas burner technology for developing and demonstrating a flexible biomass-based small scale CHP plant with 75 kw electrical output, high power efficiency and low emissions. Further, the project will aim at increasing the technology s reliability and decreasing the need for service. A control and communication system for unmanned start-up and operation of the plant will be developed. As it is described in the periodic report sent to Energinet.dk in August 2007 covering the first seven month of 2007 the objective of the project is altered, and so the effort has been put into developing, producing and Page 4 of 21

6 testing a system consisting of two separate 4-cylindred 35 kwe engine units each mounted to a combustion chamber. One of these will be the result of further development of the conventional combustion chamber and one will be a new combustion chamber based on the diluted oxidation combustion principle. The setup is outlined in Figure 1. Figure 1: New setup for plant outline. Explanation: The new setup with two separate 35 kwe engine units each mounted on a combustion chamber. Initially, the idea was to mount the old engine type (SD3E-type) on the new combustion chamber (the SEDIOX combustion chamber Stirling Engine Diluted Oxidation) and the new engine SD4F-type on the conventional combustion chamber. By employing a setup with two separate engine and combustion chamber units an increased flexibility is achieved and at the same time the vulnerability of the system is decreased. However, the overall objective of developing and testing a new Stirling engine type, combustion chamber technology and control system for remote plant surveillance and operation as it is stated in the application s project description has been sustained throughout the project. The activities of the project can be divided into three groups: 1. Research and development activities 2. Construction of components and installation of plant 3. Test operation and proof of concept. The report is structured accordingly. Page 5 of 21

7 3 Research and development activities 3.1 Gasifier A new gasifier design was applied for the 600 kw up-draft gasifier. This new design is based on the theoretical work by TEISLEV energy and the experiences with the 200 kw gasifier at the Stirling engine pilot plant in Ansager (Denmark) Modelling TEISLEV energy has developed a model for gasifier dimensioning and simulation of gasification reactions in order to calculate the composition and mass flow of the wood gas at varying operational parameters. In appendix A Modellering af modstrømsforgasser (only available in Danish) the results of the simulation is presented in detail Design Stirling DK has developed a complete a new bottom section for the gasifier where a mixture of air and flue gas is added. It is significant that this air/flue gas mixture is evenly distributed over the cross section of the reactor and the fact that the gasifier is an up-scaling from 200 kw to 600 kw makes it even more critical. An entirely new air injection system with a number of nozzles fed from a ring-formed manifold has been designed. On top of the improved distribution it also implies a reduced pressure loss compared to previous designs. Also the ash conveyer system has been modified for improved functionality. Now the ash outlet is dry, whereas it in previous designs where going through a water lock. Hereby, the ash is dry when it is exiting the gasifier which makes the following handling less complex. The height of the gasifier is reduced according to a minimum bed height. Additionally, in order to decrease the load of the reactor the diameter is increased. In the development it has been considered that the same design can be used for other gasifier sizes. Based on parametrical studies of the overall measures it is possible in the design programme to employ the same starting point for the design of 200, 400, 600 and 800 kw gasifiers that fit plants with accordingly 1, 2, 3 and 4 35 kwe Stirling engines. The result of the design process is a robust unit that is simple to produce at low costs. The final design of the 600 kw gasifier is shown in Figure 2. Page 6 of 21

8 Figure 2: Section view of gasifier. Explanation: 1...level sensor for fuel; 2... ash scraper; 3... air nozzles; 4... air manifold; 5... ash conveyor. 3.2 Combustion chamber and burner - SEDIOX In gasification based Stirling CHP plants the produced wood gas, which is a low calorific value gas (LCV-gas), from the gasification is burned in a combustion chamber. During combustion unwanted gasses like CO, NOx are formed. In order to control and lower especially NOx emissions to a minimum, diluted oxidation is regarded as a potential key technology for future Stirling CHP plants that are based on biomass gasification. Page 7 of 21

9 During ordinary combustion thermal NOx is formed in the combustion chamber in hot spots where the temperature is above 1,500 C. The diluted oxidation or diluted combustion is a combustion mode, in which combustion products (flue gas) are re-circulated and mixed into the fresh incoming fuel and air streams. This reduces the concentration of the reactants and thereby the reaction rate through avoiding the formation of sharp high temperature zones. In this respect the diluted combustion is one of the most interesting combustion technologies to meet both the targets of high energy efficiency and low pollutant emissions. This technology has already been successfully applied and exploited in industrial gas burners. In order to establish a diluted oxidation combustion concept for wood gas in combination with the Stirling engine an extensive effort has been put into the development of a new burner and a new combustion chamber. The concept is entitled Stirling Engine with Diluted Oxidation SEDIOX. A detailed description of the performed development related to the SEDIOX combustion chamber is available in appendix B Burner In the project a new burner has been developed, constructed and tested. A section view of the burner can be seen in Figure 3. The wood gas that is produced in the gasifier enters the burner through a simple tube in the centre of the burner. The wood gas tube is located in a tube where the pre-heated combustion air is led to the diluted oxidation zone. In order to avoid depositions it is necessary to ensure that the tar is not heated up in the wood gas tube inside the burner (cooling of the gas in a small range is not a problem). In the final basic design a ceramic fibre insulation tube is placed on the inside of the wood gas tube. Further a water jacket is implemented. Figure 3: Section view of SEDIOX burner. Explanation: Section view of the developed burner for the wood gas; 1 insulation between water jacket and pre heated air; 2 water jacket; 3 nozzle part; 4 thermal separation. It is acknowledged that it is significant to avoid heating of the wood gas to more than app. 75 C. This is in order to avoid deposition of tar in the burner. To cool the wood gas a water jacket was introduced on the Page 8 of 21

10 burner and further the pre-heated combustion air section (at app. 500 C) and the wood gas section are thermally separated by an insulation jacket. For more details regarding the burner see appendix B Combustion chamber When developing the new combustion chamber focus has been on the following key factors: - Increasing lifetime of critical components - Lowering of CO, NOx and UHC emissions - Improving heat transfer to Stirling engine s heater panels - Simplifying service procedures - Decreasing heat loss. The design of the SEDIOX combustion chamber proved to be extremely extensive and time consuming and it was therefore decided to develop and install an improved version of the conventional combustion chamber at the plant host and in parallel to continue the development of the SEDIOX combustion chamber. In both paths it was decided to mount the Stirling engine at the end of vertical installed combustion chamber. Hereby the handling of the engine and access to burner and joints after installation is much improved. Further, a water jacket surrounding the combustion chamber is installed, whereby the heat loss is utilised in the heat producing system, the surface temperature of the combustion chamber is reduced and the temperature in the room where the chamber is located is also reduced both leading to an improved working environment and increasing the overall efficiency of the plant SEDIOX The Danish Gas Technology Centre (DGC) has been involved in designing the SEDIOX combustion chamber in order the optimal design regarding mixture of wood gas and air and avoiding local hot spots and unburned gas passing through the combustion chamber by achieving flameless oxidation combustion. DGC has employed computational fluid dynamics (CFD) on different geometries of the chamber and investigated the resulting local gas velocities, temperatures and pressures and the heat transfer to the Stirling engine s heater panels. The work is presented in detail in appendix C1 and C2. Further, in the new design the combustion air pre-heaters are built in. One air pre-heater for each of the Stirling engine s heater panels are installed at the exit of the panels resulting in minimum heat loss from the 800 C hot flue gas and also handling (insulation of piping etc.) of hot gas. A detailed description of the development of the SEDIOX combustion chamber can be found in appendix B Conventional combustion chamber Based on experiences from previous conventional combustion chambers a new combustion chamber has been designed. The design is more compact with built-in combustion air pre-heaters. Further, the combustion Page 9 of 21

11 chamber is water cooled and there is also developed a new burner. The development activities regarding the conventional combustion chamber is described in detail in appendix D (only available in Danish) Engine interface The engine interface has been a critical point with regards to reliable long term operation as the vibrations of the engine causes wearing on the interface components. In the project a new type of pre-casted bricks have been developed. The bricks enclose the heater panels of the Stirling engine and lead the flue gas three times through the heater panels and so the heat transfer is optimised. 3.3 Re-design of Stirling engine development of SD4F engine In the project a total re-design of the Stirling engine has been undertaken. Especially the mechanics of the engine has been altered. As stated in section 2 Objectives it was decided to produce a prototype of a new 35 kwe engine. The SD4F engine is designed with the experience of the SD3E engine in mind. The intention is to make a more durable engine designed for easy and fast service. The following changes are the most significant: - Round heater to provide easier and better interface solutions. (SD4A-E has a squared heater). - Process volumes are connected in the cold end, which gives a much simpler top section suitable for less expensive production. - Larger bearings for longer lifetime and service interval, or higher output. - Compressor system for better part load efficiency and faster power alteration. - Balance rotor to minimize vibration. - Easy access to piston and rod seals, which are replaced during each service. This report is a summary of the test reports for the mechanism and cold test of the complete engine. During these test the engine is motored using the generator as a motor. Several parameters have been measured (data logged) and are used to verify the performance of the engine. Page 10 of 21

12 Figure 4: SD4F engine prepared for a cold test. The development of the SD4F Stirling engine is described in detail in appendix E. As stated in section 5 the new engine was not installed and tested and the plant host. There have neither been performed any hot tests during the project, and so the operation experiences with the SD4F engine is limited to cold tests as described in appendix E. 3.4 Control system A modular control system for un-manned control and surveillance of the Stirling engine plant has been developed. The control system has been developed by Stirling DK in cooperation with Siemens Automation who has extensive experiences with control systems for similar applications Control strategy The overall control strategy is outlined in the control diagram shown in appendix F. The load of the plant is controlled by the amount of gas sucked out of the gasifier and into the combustion chamber where it is burned and heat is transferred to the heaters of the Stirling engines. Page 11 of 21

13 The plant is equipped with one exhaust gas blower for sucking wood gas out of the gasifier and into the combustion chambers, further to produce the required the vacuum in the combustion chambers so that a sufficient amount of air (O2) is sucked into the combustion chambers and also to draw the exhaust gas through the air pre-heaters and the economizer. Further, the plant is equipped with a gasification air blower for supplying air to the bottom of the up-draft gasifier. The entire Stirling plant is monitored and controlled via the human machine interface (HMI) which is accessed on a screen either on the control cabinet on site or remotely via an internet connection. Compared to earlier Stirling plants the plant related to this project is special due to the fact that it has two Stirling engines instead of just one. This means new requirements to be met by the control system: 1. Load control on combustion chambers and engines 2. Control of one common exhaust gas blower for two combustion chamber/engine units. In the following the overall control loops will be described Control loop for wood gas valves Figure 5: Detail from appendix F - control diagram. Control loop for wood gas and combustion air valves. Explanation: The cylinder on the left is the gasifier, the yellow line is the wood gas pipe, the blue line is the combustion air pipe, the red line is the exhaust gas pipe. Page 12 of 21

14 Control loop for engine load control On Figure 6 it can be seen that the opening of the exhaust gas valve from combustion chamber #1 is controlled by input values regarding the vacuum in the combustion chamber, the highest cylinder temperature on the Stirling engine and the power output of the Stirling engine. The set point for the highest cylinder temperature is set to 650 C and the for the power output of the engine it is 35 kwe. The box with the text MIN is an analogue relay. The input to this relay is the differences between the two set points (highest cylinder temperature and power output of the Stirling engine) and the actual values of these two parameters. The difference which has the highest negative value sets the set point for the vacuum in the combustion chamber which is controlled by the opening of the flue gas valve (FGS01V020). The engine load control loop combustion chamber #2 is identical the one for combustion chamber #1. Figure 6: Detail from appendix F control diagram. Control loop for the engine load control. Explanation: The red line is the exhaust gas pipe from the combustion chamber to the combustion air pre-heater Control loop for exhaust gas blower control On Figure 7 the principle for controlling the exhaust gas blower (FGS10M010) is shown. The box with the text MAX receives the actual positions of the two flue gas valves FGS01V020 and FGS02V020. The analogue Page 13 of 21

15 relay sends the highest value to the PI regulator that sets the set point for the vacuum downstream of the exhaust gas blower which is controlled by the load on the blower. The latter is controlled by the PI regulator marked 2. The set point set to 75 % on Figure 7 is the set point for the highest value of the opening of the flue gas valves. Figure 7: Detail from appendix F control diagram. Control loop for exhaust gas blower control. Explanation: The red lines are the exhaust gas pipe, FGS10H020 is the gasification air heater, FGS10H010 is the economizer, FGS10M010 is the exhaust gas blower. The intention is to minimise the throttling on the flue gas valves and instead to lower the load on the exhaust gas blower and thereby to minimise the own consumption of electricity for the plant. Further, the applied control principle results in a smoother and more stable operation of the entire plant Remote control and surveillance In the project a remote control and surveillance system was developed. The plant is controlled through the HMI that can be accessed via an internet connection. On the HMI the plant operation can be watched and administrators can set selected operational parameters for selected components. Further, the plant can be started and stopped via the HMI. In figures 8, 9 and 10 screen shots from control system can be seen Alarms and troubleshooting The remote access to the HMI enables efficient troubleshooting as the operational personnel on site can be supervised by the relevant back office personnel e.g. gasifier or engine specialists at Stirling DK. Further, the Page 14 of 21

16 control system can send alarm messages to the operator, so critical operation conditions can be seen before they evolve and possible causes a plant shut down. Figure 8: Screen shot from HMI. Part of control system showing wood chips supply system, gasifier and ash handling system. Page 15 of 21

17 Figure 9: Screen shot from HMI. Part of control system showing combustion chamber and Stirling engine. Page 16 of 21

18 Figure 10: Screen shot from HMI. Part of control system showing water system. 4 Production of components and installation of plant The installation of the plant at Svanholm Estate was planned to be divided into two phases: Phase 1: Installation of wood chip handling system, 600 kw gasifier, conventional combustion chamber, 35 kwe SD3E type Stirling engine unit and boiler unit. Phase 2: Installation of SEDIOX combustion chamber and one 35 kwe SD4F type. 4.1 Production of components Based on production drawings prepared by Stirling DK the 600 kw gasifier and the two combustion chambers were constructed by Danstoker. The two 35 kwe Stirling engines (type SD3E and SD4F) were produced by Stirling DK. All auxiliary components have been produced by sub-suppliers based on specifications from Stirling DK. The production of the components was undertaken during the first half of Page 17 of 21

19 4.2 Plant host The collective Svanholm Estate located close to Skibby at Sjælland in Denmark was identified as host for the Stirling engine test plant. Svanholm Estate has an appropriate heating demand and the physical space for the plant installation. The installation of the Stirling engine plant is a part of a complete refurbishment of the heating system at Svanholm Estate. In August 2008 a contract between Svanholm Estate and Stirling DK taking the developmental aspects of the project into consideration was signed. The contract is included in the report as appendix F. 4.3 Installation and commissioning of plant The first plant installation phase was executed during the last three months of 2008 and commissioning was finalised in June This first phase included wood chip handling system, 600 kw gasifier, conventional combustion chamber and one 35 kwe SD3E-type Stirling engine unit. The plant layout and the process diagram of the plant can be seen in appendices F and G. The plant was put in operation July 1 st The second installation phase including installation of the SEDIOX combustion chamber and the SD4F type Stirling engine was planned to be carried out in the first part of However, due to divergences between Stirling DK and Svanholm Estate the second installation phase was never completed. 5 Test operation Due to divergences between Svanholm Estate and Stirling DK the Stirling engine plant was de-commissioned in June In the period from July 2009 to end of February 2010 the plant was in operation for 1,472 hours producing more than 43 MWh of electricity with only minor technical problems. Due to limited test facilities at the Stirling DK premises no full scale tests of the SEDIOX combustion chamber and the SD4F Stirling engine has been performed. 5.1 Gasifier In the project some very valuable operation experiences regarding the interaction between the operation of the gasifier and the rest of the plant especially the wood gas pipes Stop-and-go operation The district heating system at Svanholm did not have sufficient capacity to operate the Stirling plant continuously at full load for more than 12 hours. Then the heating system could no longer absorb the heat produced by the plant. Thus the plant was operated in stop-and-go mode with cycles of approximately 12 hours of operation and 12 hours of standby. Important experiences learned from this type of operation were Page 18 of 21

20 that it was very difficult to achieve a stable gasification process and further it caused serious problems with tar deposits in the wood gas piping Relation between temperature of wood gas and tar deposits in wood gas pipes During operation it was discovered that wood gas temperatures above app. 90 C results in tar deposits in the wood gas pipes. The water that is present in the tar fluid in the wood gas starts to vaporise when the wood gas temperature exceeds app. 85 C. Thereby the viscosity of the tar is decreased and also the tar gets more sticky both leading to critically increased tar deposits in the wood gas pipes. The solution to this issue was to increase the moisture content in the wood chips and thereby decrease the temperature of the wood gas. By applying wood chips with a moisture content of more than 35% the temperature of the wood gas can be kept under 80 C. Further, the control system sends an alarm if the wood gas temperature is more than 80 C. If the wood gas temperature is not lowered to less than 80 C within a certain period of time (e.g. 30 minutes) the plant is shut down. These experiences have also resulted in an adjustment to wood chips quality specification for all Stirling plants. Now the minimum average moisture content shall be 40% which is the moisture content of wood chips from freshly cut trees Ash discharge system On the plant in Svanholm an automatic ash discharge system was never installed. However, valuable experience was gained regarding the ash temperature and the importance of having an air tight discharge system. While operating the plant condensation of the moisture in the gasification air in the ash was causing problems with the discharge of the ash. The ash is discharge by a conveyor in the bottom of the gasifier. When the moisture in the gasification air condensed due to ash temperatures lower than the ambient temperature the conveyor could not transport the ash because the wet ash jammed the conveyor. By controlling the temperature in the ash and making sure that this is higher than the ambient temperature this problem was avoided. The temperature in the ash is increased by discharging ash at a higher frequency and thereby lowering the glow zone in the gasifier. Another issue that was identified was the importance and challenge of having an air tight ash discharge system. Different solutions regarding valves were tested but no proper solution was identified. On newer plants a knife valve is employed. 5.2 Combustion chambers and engines Even though only one engine was installed at Svanholm the operation of this SD3E-type engine still some significant operation issues was experienced on the combustion chamber and engine interface side. Page 19 of 21

21 5.2.1 Engine interface After operating the Stirling engine at nominal load (35 kwe) for a longer period of time is was discovered that the build-in combustion air pre-heaters were damaged due to high thermal loads. When investigating into this issue it was concluded that this was caused by too high temperatures in the exhaust gases from the combustion chambers. Given that the output of the gasifier and the wood chips consumption were not monitored systematically the high temperature in the exhaust gas from the combustion chamber indicates a lack of efficiency in the heat transfer to the engine. Thus, the issue was identified as a blow-by phenomenon where some of the flow of the exhaust gas was not led past the heater panels properly in order to transfer the heat to the engine. This experience has led to investigations in how to improve the design of the heater panels in order to improve the heat transfer to the heater panels both to protect the combustion air pre-heaters and even more critical to increase the overall efficiency of the Stirling plant. The solution identified is to install plates on the heaters in order to force the exhaust gas through the heater panels. This is now done on all Stirling plants. Also the design of the joints on the tubes in the combustion air pre-heaters is now improved so that they are more resistant to thermal stress. 5.3 Control system The new control system was tested and adjusted during the test operation period. The monitoring and troubleshooting via the remote access was proven to be of immeasurable value given that transportation time was minimised and diagnosing of issues could be done very efficient. This can also be directly read in the availability of the plant due to handling of operational problems in due time. Here the alarm function included in the control system showed its value. 6 Trademark registration and patent application Stirling DK has high expectations regarding the SEDIOX technology and so the concept is trademarked with the trademark no Appendix J is a screenshot from the European Union agency responsible for trademarks and designs homepage displaying the detailed trademark information. Further, a patent application for the SEDIOX combustion chamber concept has been prepared and filed to the European Patent Office (EPO) by the 21 st of September The application no. is and the answer from EPO is pending. Letter from Budde Schou patent attorneys confirming that EPO has received the patent application from Stirling DK is attached as appendix K. Page 20 of 21

22 7 Conclusion Firstly, from Stirling DK s point of view the project was a success. This is based on a number of highly valued experiences learned from the project. Further, the development of the new engine type SD4F and the SEDIOX combustion technology that was initiated in this project is now the two highest prioritised long-term R&D projects of Stirling DK. Further, a trademark is obtained for the SEDIOX technology and a patent application is filed and pending regarding the SEDIOX combustion chamber concept. As stated in section 2 the objective of the project was originally to develop an 8-cylindred Stirling engine with an electrical output of 70 kw. As the re-design of the engine was extensive enough in itself it was decided to re-design the 4-cylindred 35 KWe engine. However, the overall objective of developing and testing a new Stirling engine type, combustion chamber technology and control system for remote plant surveillance and operation as it is stated in the application s project description has been sustained throughout the project. All components for the Stirling gasification plant were produced and installed at Svanholm Estate. The plant consisted of one conventional combustion chamber and one SD3E-type Stirling engine. The plant was commissioned in June 2009 and 1,472 hours of operation and 43 MWh of electricity production was achieved before the plant was de-commissioned in February During operation the control system including remote access was tested thoroughly and with great success. The overall control principle regarding the control of the flue gas valves and exhaust gas blower is applied on Stirling plants build after this plant. Further, the remote access is also applied on all new plants. The test operation showed issues with the engine interface on the combustion chamber as the heat transfer from the hot flue gas to the engine needs optimisation. Stirling DK has since the identification of this issue developed different solutions to this which has lead to change of the geometry of the engine interface and improved heat transfer to the heater panel of the engine. All in all, the project enabled the production, installation and test operation of the Stirling plant that formed the basis of the Stirling plants produced and sold by Stirling DK currently and further, the identification of two critical long-term R&D projects to which Stirling DK has great expectations. Page 21 of 21