23rd World Gas Conference, Amsterdam 2006

Transcription

1 23rd World Gas Conference, Amsterdam 2006 SELF POWERED BOILER HOUSE: A NOVEL METHOD FOR INCORPORATING A MICRO TURBINE INTO AN EXISTING DOMESTIC ENERGY INFRASTRUCTURE FOR HEAT SUPPLY TO HOUSEHOLDS Main author Ing. F.C. de Groot Gasunie Engineering & Technology Groningen, The Netherlands Co-author B. van der Weide Gasunie Engineering & Technology Groningen, The Netherlands

2 ABSTRACT This paper describes a novel method for incorporating a microturbine into an existing energy infrastructure such that the gas consumed in the microturbine is used at efficiencies approaching 100%. To achieve this, the exhaust gas of the turbine, containing 18% oxygen is used as part of the air supply to a boiler. Thus, the useful enthalpy in the hot gases is extracted in the boiler. The burner has been modified to accommodate the hot exhaust gases from the turbine without negatively affecting the performance of the burner. Since the exhaust gases are oxygen deficient compared to air, this coupling also leads to a net reduction of 10-15% in the NO x emissions of the burner. We demonstrate the principles using a commercially available 60 kw e turbine coupled to a modified 3.25 MW gas burner.

3 TABLE OF CONTENTS ABSTRACT 1. INTRODUCTION 2. SYSTEM DESCRIPTION 2.1 Principles of operation 2.2 Operation modes 2.3 Energy balances 2.4 Operating area of the BurnerGen Pack TM 3. NET RESULTS Acknowledgement Contact information

4 1. INTRODUCTION Recent trends indicate that the delivery of electricity is becoming increasingly less reliable. As a result, there is a search for means to be less dependent on the public electricity grid. In contrast, interruptions in gas supply are very rare. In the Netherlands, for example, there has only been one systemic interruption in gas delivery in the last 30 years. Furthermore, the high power grid nearly operates at its full capacity, and it is difficult and expensive to expand this network. In the future a significant demand for self-powered systems is anticipated, as to avoid these problems. In the last few years, small turbines, which are easy to install and suitable for decentralized power generation, have become commercially available. Normally they are grid-connected, but in case of grid-failure they can switch to island operation. The efficiency of these modern micro turbines is about 30%, significantly less than the approximately 50% obtainable using modern CHP units. Therefore these small turbines are generally not used for stand-alone power generation. The flue gases leaving the microturbine have a temperature of about 300 C and contain about 18% O2. Clearly, using both the heat and oxygen in the flue gases would increase the overall efficiency of the unit. Figure 1 BurnerGen Pack TM For Gasunie Engineering & Technology (GET), it was clear that the use of microturbines for decentralized power generation must be integrated in existing boiler and burner systems. In this fashion, both the heat and excess oxygen can be used as part of the combustion air. Of course, it is also possible to increase the efficiency by using an external heat exchanger mounted directly in the exhaust gas flow of the microturbine, but the BurnerGen Pack (Burner Generator Pack) solution combines the boiler as heat exchanger and the burner to consume the remaining O 2 in the flue gases as combustion air. The BurnerGen Pack makes it possible to generate electricity locally on small scale, with efficiencies approaching 100%. See Figure 1 for a general setup. Met opmaak To reuse microturbine flue gases in existing boilers we developed an adapter which makes it possible for a burner to operate on both fresh air and turbine flue gases. In essence, this dual-air burner adapter is the heart of the BurnerGen Pack. Full scale tests in the laboratory at Gasunie Engineering & Technology were very successful.

5 We developed this new technology from a laboratory setup into a system that is suitable for market introduction for a project in Moscow, Russia, where unreliable power generation is a problem in centralised boiler houses. These boiler houses deliver heat for central heating and hot tap water. In the event of a power failure, the entire boiler house will go dark, although gas delivery is still possible. A pilot project will demonstrate the BurnerGen Pack technology in a new, self-powered boiler house. The BurnerGen Pack TM will be put into operation mid This system complies with the safety standards. 2. SYSTEM DESCRIPTION 2.1 Principles of operation Schematically configured in Figure 2, the main parts of the BurnerGen Pack are: Microturbine, for this project a Capstone C60; Standard forced draught burner, Oertli Induflame Cib612; Specially engineered burner head, suitable for retrofitting existing burners, known as a low NO x dish burner; Dual-Air Burner adapter, which makes the dish-burner suitable for operating with fresh air and hot flue gases from the microturbine. Figure 2 Schematic overview of the BurnerGen Pack TM The Dual Air Burner adapter is mounted between the standard fan burner and the boiler front. Fresh combustion air is directly fed into the burner head by the (existing) fan burner. The turbine flue gases are supplied to the burner by the Dual-Air Burner adapter in such a way that the flue gas resistance is low, below its limits (<20 mbar). This will avoid a reduction of the electrical efficiency of the microturbine. The construction of the adapter makes it possible to operate the burner in the pure fresh air mode as well in the mixed air mode (fresh combustion air and flue gases). In mixed air mode, the amount of cold air can be reduced to have the same gas-air ratio as in the fresh air mode. Thus all the flue gases are used for combustion. See Figure 3 for a picture of the prototype in the laboratory of GET. Because of the low oxygen content in the microturbine flue gases, NO x is reduced by 10-15%.

6 Figure 3 Prototype BurnerGen Pack tested in GET laboratory Tests have shown that the operating area of the BurnerGen Pack can be almost the same as a normal stand-alone low-no x burner. The flame stability over the entire operating area is good; the gasair ratio can be varied over a wide range, and CO remains <10ppm and Nox < 60 mg/m 3 (n) (3%O 2 ). 2.2 Operation modes The system is developed for three operating modes: Fresh air mode only; The micro turbine is switched off or there is no grid connection; Dual Air Burner mode: both the burner and the microturbine are in operation. Here, the microturbine is always at full load (60 kwe); Turbine mode only: the flue gases of the micro turbine are led into the boiler by the Dual-Air Burner adapter, with the burner switched off. The boiler is used as an extra heat exchanger to extract the useful enthalpy of the hot flue gases. The 57 kw e produced by the micro turbine is, in practice, enough to operate the gas burner, the control equipment, the hot water circulation pumps and the auxiliary equipment in the boiler house. The microturbine is equipped with its own backup batteries and a switch unit for starting up after failure of the public electricity grid. The switch unit controls the switching from grid-connected to island-operation in a load (electrical power) following mode. 2.3 Energy balances A Sankey energy flow diagram of the BurnerGen Pack is given in figure 4. A gas compressor will be necessary in case the gas delivery pressure is below 5 barg. The gas compression takes, unfortunately, 3 kwe. The overall efficiency with gas compression is about 93%, without gas compression about 95%.

7 Figure 4 Energy flow diagram microturbine 2.4 Operating area BurnerGen Pack TM Figure 5 shows the operating area in fresh air mode and in the combined burner and turbine. The blue and purple lines in Figure 5 indicate the operating area of the BurerGen Pack TM. The red lines the No x formation. The green arrow indicates the Nox-reduction by the BurnerGen Pack TM. The blue arrow in Figure 5 indicates that in the mixed air mode cold air can be reduced to have the same gas-air ratio as in the fresh air mode. Thus all the flue gases of the microturbine are used for combustion. The yellow arrow indicates that at minimum load some extra cold combustion air is needed, supplied by the burner fan, to maintain a stable primary flame at the disk of the burner. Figure 5 Operating area BurnerGen Pack TM

8 Figure 6 gives a unique view of the staged combustion. The photos were made through the windows of our optically accessible combustion chamber. See also Figure 4 test setup. Figure 6 Side and front view flame disk burner 3. NET RESULTS The net results of the development of the BurnerGen Pack TM are: Extra gas used by the microturbine is converted into electricity with a very high efficiency of 93% (without gas compression 95%); NO x reduction of 10-15% if the flue gases of the microturbine are added to combustion air; The microturbine and burner can be operated independent of each other. At minimum heat demand, the boiler is used as a heat exchanger for the microturbine flue gases. The enthalpy of the hot flue gases is then extracted in the boiler; The system is suitable for retrofitting in existing boiler installations; The safety requirements for industrial forced draught burners are fulfilled; Field tests are foreseen mid 2006 in a Russian domestic energy infrastructure for heat supply to households. Acknowledgement The development of the BurnerGen Pack TM has been carried out in close cooperation with the Burner Manufacturer Oertli Induflame.The implementation in a Russian Boiler house is carried out in cooperation with Banking Production Centre in Moscow (recipient) and the owner of the boiler house Mytischi Teploset (Moscow region). The project has been made possible by EVD, an agency of the Dutch Ministry of Economical Affairs, within the framework of a programme for high level technological cooperation with Eastern Europe.

9 Contact information Gasunie Engineering & Technology Energieweg AN Groningen P.O. Box MA Groningen The Netherlands T +31 (0) F +31 (0) get@gasunie.nl Web: