Landmark installation for micro-CHP6 May 2002
Very high operating thermal efficiency is expected of this tri-generation system, one of the first to be powered by a microturbine, at a hospital in Barcelona, Spain. Staff Report
This tri-generation system, which has been developed in collaboration with Gas Natural, one of Spain's leading gas suppliers, and installed in collaboration with the company's Spanish distributor Icogen SA, provides electrical power, heating, and cooling for a morgue attached to a major hospital in the city of Barcelona. It is one of the earliest examples of such a system.
The first tri-generation system to be developed by Bowman, a UK company which has found a niche in the market as a microturbine co-generation specialist, it comprises a TG80CG Turbogen generating 80kWe electrical energy coupled to a waste heat boiler providing a heat output of 150 kW thermal energy. This in turn is coupled to a Yasaki model Aroace WFC-30R hot water powered 115 kW absorption refrigeration unit supplying chilled water. The thermal output provides heating and air conditioning for the building, while the electricity generated is consumed within the complex. Any excess is sold back to the grid.
The combined heat and power combination is being offered as a standardised unit by Bowman which is developing its Turbogen family of small scale compact generation systems ranging from 25 kWe to 80 kWe, for distributed power generation and for mobile applications. These systems are based on compact gas turbines (microturbine engines) and high speed generator technologies (turbo-alternators) together with associated power electronics for control and power conditioning.
Bowman is specialising in supplying CHP systems where the exhaust heat is recovered to provide hot water, or air conditioning when coupled with an absorption chiller. With levels of efficiency up to 80 per cent attainable in theory, the payback period can be very short, in addition to other benefits of availability and reduced emissions.
The morgue itself is a modern construction of concrete and steel. As the Bowman unit is roof-mounted, directly above one of the "Chapels of Rest", there were initial concerns about noise from vibration. However once the unit was installed and run up, it was clear that the noise attenuation components of the unit ensured that there would be no such problem. The involvement of Gas Natural has apparently been pivotal to the success of the scheme. Initially, there was no gas to the site, so a diesel-powered option was first considered. When this was rejected, Gas Natural became involved, supplying gas pressurised at 6 bar to the site. But the company has also expressed great interest in the project data, for its own promotion of co- and tri-generation systems throughout Spain. The technology used in this scheme suggests potential for a range of applications including supermarkets, frozen food retailers and hotels.
The turbo-generator unit at the heart of the system is flexible in operation. It can run on a variety of fuels including natural gas, lpg, propane and butane; it can be utility connected or used in island operation, for baseload or peak shaving or load following modes. The conditioner/controller allows for power export options. Acoustic performance is measured at 77 dBA at 1 metre.
The turbo-alternator comes from a family of units with output options from 20 kW to 1.5 MW. It consists of a rare earth brushless 4-pole permanent magnet rotor type alternator coupled directly to the turbine shaft. The alternator doubles as both starter and electrical generator and so obviates the need for a starter motor, while its high speed capability eliminates the need for a speed reduction gearbox. The unit's high efficiency (98 per cent) is achieved primarily through control of current losses - ohmic, core, fluid dynamic and stray eddy losses - and its high power density leads to a compact footprint. It can operate in temperatures from -10 °C to 45 °C, offers oil, water or air cooling options and is claimed to be highly reliable and rugged.
The CHP unit
The TG80 CG unit consists of three main functional areas; namely heat recovery, the microturbine engine and the control and power electronics. These are shown left to right in the schematic on page 23.
The heat recovery bay contains the heat exchange components that provide the CHP heat transfer capability. Use of the turbine's exhaust heat, after the recuperator has taken its share, helps improve operating efficiencies to around 80 per cent, in contrast to the 20 per cent or so of the turbine alone. In the maximum configuration these components consist of a gas to gas recuperator type heat exchanger with bypass valve, a gas to water waste heat recovery unit (the 'boiler') and an oil cooler.
The engine bay section contains the combined micro turbine and alternator, coupled directly and running at the same shaft speed of 68 000 rpm, together with associated systems to provide the fuel supply, air supply and lubrication/cooling oil for the turbine and alternator.
Elliott Energy Systems (of Florida, USA) manufactures the turbo machinery and the alternator. Power conditioning and control systems are provided by Bowman. Gas fuel is pressurised to 6 bar using a V05G gas compressor unit supplied by Bowman and designed specifically for MTG/CHP systems. It employs a rotary vane compressor and simplified gas/oil separation system. To minimise power consumption, delivery pressure from the compressor and gas flow rates have been matched to those of the Turbogen.
The control and power electronics bay contains the local operator control panel and electrical interfaces for the 3-phase power output, and auxiliary power input and remote control. It monitors and controls the whole system and provides conditioning and switching of the output power supply. Conditioning circuitry is based on IGBT (insulated gate bipolar transistor) semiconductor technology.
Heating and cooling
The unit provides for the essential cooling operations of the morgue, as well as chilled water for the building's air-conditioning. The waste heat boiler (essentially a gas to water heat exchanger) serves the building's hot water system and also provides heating via the central heating system in which the integral heat exchanger acts as lead boiler. Alternatively hot water is switched to the chiller when cooling is required. Heating and cooling could in theory be provided simultaneously, but in line with local practice hot water is delivered either to the chiller or to the heating circuit; the valving arrangement is not automatic, but manually operated. Some of the cooling load - that applicable to the body storage area - is met by electrically powered unit air conditioners located in the individual bays. Chilled water air conditioning units serve the general areas of the building.
Although there are no installation performance data available at this point, a performance criterion of sorts exists in the CHP Quality Assurance scheme being promoted by the UK government. It provides a methodology for calculating a quality index (QI) for CHP schemes on the basis of their energy efficiency and environmental performance. The QI in this case (see Table 3) came out at 109, better than the 'good quality' rating of105.
TablesTable 1. General TG80 CG performance specification Table 2. Yazaki Water Fired Absorption Chiller Aroace WFC-30 R Table 3. Cogeneration system UK quality index for the TG80CG