13 Steam Turbine Equipment and System
13.1 Steam Turbine Equipment
13.1.1 Steam turbines shall be selected for power plants according to the following requirements:
1 The capacity and quantity of cogeneration turbines shall be determined according to the magnitude and property of heating loads following the principle of determining the power generation based on heating loads.If the conditions permit，steam turbines with larger capacity and higher parameters shall be preferred.
2 Condensing turbines should not be used for small power plants.In remote areas which are inaccessible to the power grid or the areas without electricity supply，if there are no resources for small-scale hydropower and renewable energy and convenient transportation conditions but there are rich coal resources，appropriately sized condensing turbines or extraction condensing turbines may be installed taking into account the actual conditions there.Also，in areas which are inaccessible to the power grid and powered by small-scale hydropower stations and where coal resources are available，condensing turbines or extraction condensing turbines with appropriate capacity may be installed as well to supplement the electricity supply during dry season.
3 In arid areas where drought exponent is greater than 1.5，air-cooled turbines should be used.
13.1.2 The optimal configuration scheme for the cogeneration turbines shall be determined through technoeconomic comparison according to the heating load curve characteristics based on the heating loads verified through investigation.
13.1.3 Cogeneration turbines shall be sized in compliance with the following requirements:
1 For cogeneration power plants which supply continuous and stable heating loads all the year round，back pressure turbines shall be selected preferably according to the basic heating loads of the whole year.
2 For cogeneration power plants which supply partial continuous and stable heating loads and partial variable heating loads，back pressure turbines or extraction back pressure turbines shall be selected to supply basically stable heating loads，while extraction turbines shall be selected to supply variable heating loads.
3 The back pressure turbine should not be used for the first generating unit installed in a newly-built cogeneration power plant.
13.1.4 The thermalization coefficient of a cogeneration power plant can be selected as follows:
1 The thermalization coefficient of a cogeneration power plant should be less than 1.
2 The thermalization coefficient must be determined through techno-economic comparison according to the actual local conditions while comprehensively taking into account various factors，and should comply with the following requirements:
1）For cogeneration power plants with a single unit capacity of not larger than 100MW and serving both industrial and domestic heating loads，the thermalization coefficient should be less than 1.
2）For cogeneration power plants mainly serving industrial steam heating loads all the year round，the thermalization coefficient should be 0.7-0.8.
3）For maturely developed areas（namely，the construction works approach the end，and nearly zero building area is newly added each year）where the heating loads are dominated by domestic heating，the thermalization coefficient should be controlled within 0.6-0.7.
4）For areas under development（namely，each year a certain number of new buildings requiring heating loads are newly put into service）where the heating loads are dominated by domestic heating，the thermalization coefficient can be larger than 0.8 and even approaches to 1.
5）Determination of the thermalization coefficient shall involve analysis on the characteristic of heating loads.A high value shall be taken for heating loads with high annual utilization hours and stable daily loads，while a low value for heating loads with low annual utilization hours and varying daily loads.
13.1.5 In areas where the heating loads vary significantly with seasons or between daytime and nighttime，the following heat supply mode may be adopted to accommodate the peak demand:
1 Supplement the heat supply by temperature and pressure reducing devices with the aid of the margin capacity of the boilers.
2 Supply heat through cooperation between the cogeneration turbines and the peak load boiler house.
3 Supplement the heat supply with selected heat customers owned coal-fired boilers characterized by a large capacity，high heat efficiency and less operating time.
13.1.6 A heat supply system either in parallel connection or serial connection may be provided to connect peak load boiler house to the cogeneration power plant，depending upon the results of techno-economic comparison.And the following requirements should be met:
1 If parallel connection is adopted，the peak load boiler house should be built inside or nearby the cogeneration power plant.
2 If serial connection is adopted，the peak load boiler house should be built at the heat load center or at the far end of the district heating system.