Study On Properties Of Heating System Using Intermediate Steam Extraction To Inject Exhausted Steam For Heat Supply

The central heating system based on cogeneration can realize the energy cascade utilization and applying the temperature phase, which is of great significance to the realization of energy conservation and emission reduction in central heating industry. With the rapid development of economy and the speeding up of the urbanization in our country, the heating load has increased dramatically and the extended capability of heat source cannot keep up with the demand of heating load, resulting serious heating shortage problem. The current cogeneration mostly use the extraction condensing unit with high steam extraction data. At the same time, there is a large cold source loss in the turban exhaust, influencing the improvement of heat utilization efficiency of unit and the advantages of cascaded utilization of energy in cogeneration.Based on the analysis of the heating load characteristic of ordinary extraction condensing unit, referring to the problem that increase high parameter extraction to improve the heating capacity may lead to the reduce of generated energy, proposed the modification schemes of using the turbine exhaust to improve heating capacity for cogeneration heating system:Use the high pressure heating extraction to drive the steam injector to inject the exhausted steam from the turban, then make use of the mixed steam for heating. On the premise that the generated energy decrease slightly, this system can reduce the cold source loss and the high quality steam extraction, improve the heating capacity, realizing the efficient utilization of energy.Based on one 25MW extraction condensing heating unit, use the software LabVIEW for simulation modeling of the modified unit using intermediate steam extraction to inject exhausted steam. And simulate in different conditions, the results as follows.Under the rated heating load condition, in the modified unit with the increase of ejector coefficient, the quantity of the third extraction, exhausted steam and heating steam increase, but the enthalpy and quantity of fourth, fifth and sixth extraction and the fourth and fifth exhausted steam decrease. As the ejector coefficient increases from 0 to 0.4, the generated energy of modified unit decreases a little (about 4.88‰). The unit heat output and heat utilization increase significantly, with 30.6% increase of heat output and 17.33% increase of heat utilization. At the same time, standard coal consumption rate decreases from 1.276 kg/kW·h to 0.199 kg/kW·h, decreasing about 28.02%.At the settled ejecting ratio with the increase of heating extraction quantity, the third extraction increase, but the enthalpy and quantity of fourth, fifth and sixth extraction and exhausted steam. Also the generated energy and standard coal consumption rate decrease gradually, but the heating load and the thermal utilization increase gradually. When the ejecting ratio U=0.10, with the increase of heating extraction quantity from 20 t/h to 80 t/h, the difference of generated energy before and after modification increase gradually. But the growth of heat quantity keep around 7.7%, the standard coal consumption rate increase from 0.005 kg/kW·h to 0.028 kg/kW·h and the heat utilization increase from 0.6% to 9.4%. We can see that in the modified unit when the steam ejector is settled, with the increase of heating extraction quantity, the improvement of energy efficient becomes more significant.Study shows that the heating mode of using intermediate steam extraction to pump exhausted steam can improve the thermal economic index of the unit, and get better comprehensive economy benefit.