An ambitious fuel switching project undertaken by Alstom has created the first power station in China operating with LNG as its primary fuel and has enabled the owner to return to profitable power production.
Peter Trentini, Alstom Power Service, Switzerland
China is bringing on line as much as 1 GW of power generation capacity each week to keep pace with its rapidly expanding industrial economy. Many of the country’s power stations are oil fired and hence China, like many countries, has been affected by the steep rise in oil prices. Electricity prices in the country are relatively stable because of government regulation, but the rising price of oil is putting pressure on power producers. Officials in the Chinese province of Guangdong are now advising that smaller scale oil fired power stations be replaced by larger coal fired power plants.
It is against this background that one independent power producer, Shenzhen Meishi Electrical Power Systems Co. Ltd, decided to convert its oil fired power station to instead run on Liquefied Natural Gas (LNG), a more economic and more efficient fuel.
In May 2005 the Meishi combined-cycle power plant, in Shenzhen, Guangdong province, returned to commercial operation after the successful completion of an ambitious fuel conversion project. It became the first Chinese power plant to use LNG as primary fuel and several other plants are now considering the possibility of LNG conversion.
Independent power producer, Mieshi Electrical Power Systems decided to convert its oil fired power station to run on LNG instead
The pioneering project was part of an improvement plan implemented by the plant owner to return Meishi to sustained profitability. Since 1995, Meishi’s GT13E2 gas turbine had been using diesel oil to generate electricity. The switch from diesel to LNG has significantly lowered fuel costs and additional savings have come from the efficiency increase that LNG firing brings to the gas turbine. Overall power output has also shown a moderate increase.
There were also major environmental benefits from using LNG as opposed to diesel. NOx emissions have been considerably reduced and, because LNG consists mainly of methane (CH4), it produces no sulphides or other particulate matter after combustion, which helps reduce smog and improve the city’s air quality.
It was very important for the plant owner to demonstrate to the regional government that the rejuvenated plant could reliably produce electricity to help reduce the burden on Shenzhen’s electricity supply system, especially in the summer months of peak demand. Shenzhen is a region with 12 million inhabitants and is in fast development. It is situated to the north of, and is in competition with, Hong Kong.
Meishi’s success will also play an important role in the promotion and wider application of LNG technology in the Chinese power market, as the project has received substantial publicity in the Chinese media.
Currently there is no local LNG distribution point and consequently the fuel needs to be trucked 4300 km from Xinjiang to the plant. LNG is transported in specially designed vessels and stored in tanks on site. LNG is about 1/600th the volume of natural gas at standard temperature and pressure, making it cost-efficient to transport over long distances where pipelines do not exist. However, the choice of LNG at Meishi was also influenced by the fact that a gas pipeline and terminal is being constructed at Shenzhen and is scheduled to come into operation in mid-2006.
Shenzhen Meishi Electrical Power Systems approached Alstom to carry out this project, knowing that the company has considerable experience in all types of complex power projects. One of the criteria that was extremely important for the customer was that the plant be converted quickly, so that electricity production could resume in the shortest possible time.
Alstom was responsible for the management of the project, along with engineering and procurement. To cut time, it was decided to leave the existing fuel oil system in place. To minimize the investment cost, as much as possible of the existing equipment was used for the new system.
Fuel system adaptation
The conversion work centred on the fuel gas system, which was the core element of the conversion project alongside the engine operation adaptation. The fuel gas system consists mainly of the fuel gas flow meter, fuel gas main shut off valve, the fuel gas control valve block and the fuel distribution system on the gas turbine, along with associated piping.
The fuel gas flow meter measures the fuel gas flow to the gas turbine and was installed upstream of the fuel gas shut off valve. The fuel gas shut off valve was designed according to Alstom’s detailed specification and consists of three elements, a main valve, a relief valve and a strainer, to filter out larger particles from the gas stream.
Connected to this is the fuel gas control valve block, which was designed and engineered by Alstom and manufactured by sub-suppliers. The control valve block regulates the gas flow while the machine is in operation. It consists of a trip valve, a relief valve, a pilot control valve and two premix control valves. The gas turbine speed during start up and the load after synchronization are controlled by the pilot and premix control valves.
The total time for the conversion project was seven months – half of the originally planned total project time
After speeding up the gas turbine to ignition speed, the pilot control valve opens wide enough to supply the necessary amount of gas to some of the burners to be ignited by the ignition flame.
After ignition, the pilot control valve opens according to the starting programme and after synchronization the pilot control valve opens further to increase the GT load. At around 50 per cent load the pilot control valve is closed completely and the unit is operated by the premix burners. Above 50 per cent the second premix control valve opens and the remaining burners are ignited.
To ensure safe operation, the control valves and the trip valve close immediately after an emergency trip of the gas turbine, the relief valves open and the gas system depressurizes downstream of the main shut-off valve.
The burners are Alstom’s EV (EnVironmental) dry low NOx burners, fitted as standard to the GT13E2 range. This engine is characterized by the successful matching of Alstom’s EV burner with a fully annular combustor.
The Meishi plant and LNG station
The fuel distribution system was designed and engineered by Alstom. The existing fuel distribution system, originally supplied for fuel oil only, was extended by a standard module for the optimum operation with fuel gas. The fuel distribution system feeds the gas to the 72 EV burners at a flow rate corresponding to the demanded power output and in the necessary condition for operation. The fuel distribution is divided into six sectors, each feeding 12 burners.
All new signals for the newly installed components related to the fuel gas system had to be integrated into the existing control system. The control system was further enhanced to provide the optimum efficiency of the gas turbine and provide stable operation over the entire load range, especially with regard to reducing emissions to a minimum. In addition to that, all necessary safety signals from the LNG supply system, were integrated into the gas turbine control system.
The total time for the conversion project was seven months. This was half of the originally planned total project time. This substantial time reduction was the result of the strong partnership and excellent co-operation by both companies to realize the project in the most successful way. The division of work between the two companies was established in consideration of their individual strengths, leading to a smooth execution of the project.
The Meishi plant is currently producing power output of around 236 MW at an ambient temperature of 28°C. It operates as a peaking unit for about 16 hours per day. The plant is configured with a 166 MW GT13E2 Alstom gas turbine and a 70 MW steam turbine installed in 1995. The plant has been running reliably and safely, giving the expected performance since the project was completed and handed over to the customer.
Shenzhen Meishi Electrical Power Systems has rated Alstom’s performance of the overall project as excellent, in terms of technical support, project management, documentation and acceptance tests/project close-out. Alstom will continue to provide services to the plant, including regular inspections, as well as performance upgrades for the gas turbine and for the combined cycle system including heat recovery steam generator (HRSG) and steam turbine.