Study of the Feasibility of the Operation of Steam-driven Pumps for a Heat Supply Air-cooled Unit

In the light of the situation that the heat supply and extraction pressures of heat supply air-cooled steam turbines are excessively high in most cases,especially those of the condensing type ones which had been modified for heat supply,proposed was a mode for the operation of steam-driven pumps during which the steam extracted from the aircooled steam turbines was first introduced into back pressure type steam turbines to do work and drive the feedwater pumps and then to provide heat. With a real unit in a power plant in Shanxi province serving as an example,a calculation program was prepared to conduct a check calculation of the exhaust steam pressure and the steam flow rate extracted for heat supply under the rated load operating condition and the off-design operating conditions respectively. It has been found that with the heaters in the heating network serving as the heat sink for the back pressure type steam turbines to drive the feedwater pumps,the output power of the back pressure type steam turbines can be stabilized,capable of meeting the power demanded by the feedwater pumps and not influencing the heat supply process.Compared with the cost-effectiveness of the operating mode in which motorized pumps are adopted,that of the mode in which steam-driven pumps are employed is better. At the rated main steam flow rate,the net heat rate of the unit will drop by about 182 kJ / kW. h. The calculation result of the investment repayment period shows that if the abovementioned operating mode is adopted,all the modification cost and investment in the equipment items can be paid back in around three years.