Two trigeneration plants serving very different host sites in Europe illustrate the advantages of producing not just heat and power from on-site cogeneration plants, but, with additional cooling plant, cooling energy too. Both applications use gas engine gensets and absorption chilling machines.
HIGH-PRECISION ENERGY SUPPLY TO MICROCHIP MANUFACTURER
DEUTZ Power Systems GmbH & Co. KG has now supplied nine generating sets (gensets) based on its TCG 2032 V16 natural gas engine to the Energy Supply Centre II (EVC II) of Energieversorgungscenter Dresden-Wilschdorf GmbH & Co. KG. The last three gensets were installed in late October 2006, together with six gensets from the same series originally installed in April 2005. Now that the final configuration for Phase 2 is complete, EVC II is able to deliver 35 MW of electricity, 38 MW of heat and 53 MW of refrigeration to the semiconductor plant, Fab 36, of the microchip manufacturer American Micro Devices (AMD) without interruption.
Figure 1. Schematic of energy production at the EVC II in Dresden
The core technology consists of:
- nine lean-burn gas engines (each 3.9 MWe), each with a multi-stage heat train producing steam (each at 1.74 MW) and hot water (each at 2.56 MW)
- three double-effect absorption chillers (each at 4.8/5.8 MW)
- two single-effect absorption chillers (each with 3.2 MW)
- five turbo-compression chillers (each at 4.8/5.9 MW)
- 14 cooling towers (each at 6.5 MW/cell)
- two steam boilers (each at 11.7 MW)
- four energy accumulators – together in a power condition device (PCD) – with 6.5 MWe in total
- main switchboard with 20 kV and 0.4 kV.
This high-precision plant can achieve an energy efficiency of up to 85% due to its highly developed technology and the use of natural gas as a fuel. Low carbon dioxide (CO2) emissions are a further advantage. Sufficient energy is produced to supply a city of 150,000 inhabitants with electricity, heating and refrigeration.
According to its operator, the design of this plant is unique. AMD requires the utmost precision, purity, reliability and security for the production of its 300 mm wafers. The specially configured kinetic storage PCD is provided to accomplish the requested power quality of ±8% on the 20 kV voltage system. Each of the combined units has a flywheel coupled with an engine-generator combination. With this technology, the PCD is capable of absorbing as well as delivering energy, and can thus compensate for load variations in the electricity consumption of up to 6.5 MW over five seconds. The PCD also makes it possible to comply with a tolerance of ± 1% in the 50 Hz frequency range.
AMD Dresden’s Energy Centre II (shown here) uses trigeneration to supply electricity, heat and refrigeration for the AMD microchip manufacturing plant (M&W Zander FE GmbH)
The production of heat and cooling in EVC II is no less demanding: Within the plant heating system, the outlet water of the engines is heated up to 95°C. The allowable temperature tolerance is 1°C. The heat of the gas engines is also used for the absorption chillers. The hot water at 80°C (+3, -1°C) is used for space heating as well as to heat ultra-pure water. Warm water at 32°C (+4, -2°C) heats the air, which is pumped in from outside and then dried with cold water at 5°C (±0.5°C). The air in the clean room is cooled by cold water at 11°C (±1°C).
The four-stroke Otto gas engines also had to be adapted to meet the high requirements for power quality. Frank Feyand, project manager of DEUTZ Power Systems states: ‘For the three new gensets, we had to use a bigger base frame and a bigger generator, which increased the total weight up to 75 tonnes.’ The first six gensets have been running to full capacity; the seventh genset has been operating permanently since January 2007 and the other two will come into operation later this year.
The natural gas engine at the Energy Supply Centre
The power cut in November 2006, which affected large areas of Western Europe, had no impact on the EVC II. ‘In the East, an island of too much power has been building up’ [i.e. power in the local grid could no longer be allocated to customers], comments the general manager, Kai Brinkmann. ‘The frequency was exceeding the tolerance. That’s why we switched on to island operation [emergency power supply, independent of the local grid] for half an hour – the first time ever. It worked absolutely perfectly. Normally, the EVC II’s power supply is provided through the system interconnection with the 110 kV grid of the local net. But if the power frequency in the 50 Hz range changes more than 1%, it automatically switches to island operation.’
The reliable cogeneration plant technology of the general contractor, M&W Zander FE GmbH, already meets the high standards of AMD’s Global Climate Protection Plan (GCPP) set by the company for 2007: more than 200 MWh of electricity are saved annually and, in 2005, this meant a reduction in CO2 emissions equivalent to 22,000 megatonnes of coal equivalent (MTCE).
TRIGEN PLANT SUPPLIES UNDERGROUND COOLING FOR COAL MINE
Since 2000, the Polish coal company Spólka Energetyczna Jastrzebie S.A. (SEJ) has operated a trigeneration power plant with gas engines from DEUTZ Power Systems at its coal mine in Pniówek, Upper Silesia. This project from the German company, STEAG Saar Energie AG – together with its subsidiary, SFW Energia in Gliwice – is unique owing to the use of the gas from the coal mine gas not only for electricity production but also for cooling the underground galleries in the mine. The combined heat and power (CHP) plant converts 13 million m3 per year of mine gas (corrected to 100% methane) into 7 MW of heat and 6.6 MW of electricity, as well as cooling energy of 5.7 MW aboveground and 5 MW underground. This results in a total efficiency of more than 80%.
Gas from the Pniówek coal mine in Poland’s Upper Silesia region is used for both electricity production and cooling the mine’s underground galleries (STEAG Saar Energie AG)
The rock mass of the Pniówek coal mine is at a high temperature and the mine has high concentrations of methane (CH4). According to Polish law, employees can only work a shift of 7.5 hours underground at an ambient temperature of 28°C. If the temperature is between 28°C and 33°C, working is only allowed for up to 6 hours and, at temperatures over 33°C, working is not permitted.
The coal seams in Pniówek are at a considerable depth, which aggravates the mine’s climatic conditions. Without chilling, the temperature in the underground at a depth of 705 m is approximately 25°C. The ambient temperature of the rocks is 31-35°C. At a depth of 830 m, the temperature in the mine is 27°C and the ambient temperature of the rocks is 36-40°C. At a depth of 1000 m, the temperature in the mine is 29°C and the ambient temperature of the rocks is 41-45°C.
The cooling system at Pniówek is used for water cooling and mine operation (STEAG Saar Energie AG)
Before the CHP plant began operating, the temperature of the air exceeded 28°C for 750 workers employed in longwalls and headings. According to an analysis by the University of Mining and Metallurgy in Krakow, cooling systems with 5 MW cooling power are necessary at 830 m to maintain an extraction rate of 14,000-15,000 tonnes per day; at a depth of 1000 m, 10 MW of cooling power would be required.
The methane-containing mine gas, which is released during the mining process underground, poses a significant risk to the coal miners because of its explosive potential. In addition, the emission of methane aboveground is critical for humans and the environment because the greenhouse effect of CH4 is 21 times that of CO2. Between 5 and 10 billion m3 of methane are emitted each year to the atmosphere from decommissioned coal mines in Europe.
The utilization of mine gas for power generation therefore has benefits for industrial safety as well as ecological and economic benefits. Utilization of the methane gas at Pniówek results in a reduction of CO2 emissions of approximately 250,000 tonnes per year. Its substitution for other fossil fuels also results in less use of existing resources.
The power engineering-cooling system at the mine is based on two integrated gas systems and electric generating units. Each unit contains two absorption cooling machines and one compression cooling machine. The heat for the absorption cooling machine is generated by methane-based CHP plants based on coal mine gas, each with an electric power of 3.2 MW per plant.
The conditions in Pniówek are favourable. The gas capacity is 238.2 m3 methane per minute, of which 97 m3 per minute (41%) is removed into the methane drainage pipeline and 141.1 m3 per minute is discharged with air into the atmosphere.
About 13 million m3 per year have been utilized since the two gas engines became operational, thus reducing the amount of methane from the mine posing a risk to the environment. The effectiveness of removed methane usage increased from 64% to about 95% in 2000. About 25 m3 of methane per minute are used as fuel for the two four-stroke gas engines (TBG 632 V16) supplied by DEUTZ Power Systems.
Figure 2. Schematic of the interconnected power-cooling system at the Pniówek coal mine
The two engines have now operated for 50,000-55,000 hours with the highest availability and reliability. The TCG 2032 (the new model name for the TBG 632 V16) is the only engine in the world operating with mine gas with a methane content down to 25%. The DEUTZ V12 and V16 engines (i.e. 12 and 16 cylinders) have a unit output range of 3000-4000 kW at 1000 rpm/50 Hz; 2928-3916 kW of heat are also available. The engines drive the generators with 3194 kV at 0.3 kV and 50 Hz per unit.
The heat produced by the process is converted chemically into cooling. Part of the power, produced by the generators, is used for water cooling and to operate the screw compression coolers. The rest is used in the operation of the coal mine.
Water is the cooling medium in the central air conditioning system, where it is passed through absorptive bromine- lithium coolers at a rate of 300 m3 per hour. In a warm water cooler, the water is cooled further from 18°C to 14.5°C, and then from 14.5°C to 4.5°C in a hot water cooler. In the next step, a compression screw cooler cools it down to 1.5°C.
The water is then transported to a depth of 830 metres through insulated pipelines with a cross-section dimension of 300 mm. A triple-chamber pressure lock is used to transport the water in the shaft system. The use of three water chambers ensures a continuous flow with only slight pressure fluctuations. The chambers are filled cyclically with hot and cold water. While the cold water is transported to the second cycle, the hot water is loaded back to the first cycle. The flow of water is induced by two pumps and controlled by valves in all three chambers. The triple-chamber pressure lock means that the efficiency coefficient of the air conditioning system is improved and the temperature rise is slight (0.5°C).
The 5 MW air conditioning system at the Pniówek coal mine was installed in two stages. The first stage, with a cooling power of 2.5 MW, was handed over for use in June 2000. Work on the second stage, with a cooling power of 5 MW, began in the second half of 2000.
‘On 9 May 2006, the order for the third extension of the plant was signed in Pniówek,’ explains Wolfgang Treutlein, head of sales and marketing at DEUTZ Power Systems. ‘With this extension, the total output of this plant will be increased to more than 10 MW of electricity and 11 MW of heat. For the extension, the customer chose another gas engine set of type TCG 2032 V16.’
The Polish coal company which operates a trigeneration power plant at its mine in Upper Silesia
Compared with cooling systems based on compression coolers, the interconnected power cooling engineered-cooling system is characterized by greater expenditure in the first stage of investment. A return on investment is expected after five years.
The energetic, economic and ecological effects resulting from the use of the methane gas are summarized as follows:
- a reduction in methane emissions to the atmosphere of about 8 million m3 per year
- additional methane consumption of about 13 million m3 per year
- methane removal of approximately 52 million m3 per year
- sale of cooling is about 41,000 MWh per year
- sale of electrical energy is about 42,000 MWh per year
- reduction in purchase of electrical energy of about 42,000 MWh per year
- improved working conditions and increased productivity by limiting the number of walls in the mine where the temperature exceeds 28°C.
Pedro Vodermayer is Head of Sales for gensets and co-ordinator of EU subsidiaries at DEUTZ Power Systems GmbH & Co. KG. e-mail: email@example.com