Key Technologies Analysis To Co-operation Heat And Power System Under Off-design Working Conditions

Recovering turbine exhaust steam’s excess heat has become a promising way to heat the urban district heating network,which can also improve thermal plant unit’s efficiency,especially under the circumstance that fossil thermal plants go peaking-shaving for the power grid.This manuscript was completed with the core of coal-fired plants going peak-shaving to the power grid,according to "energy cascade utilization".Feasible region of heat and power was established,meanwhile co-operated heat and power(CoHP)model was evaluated in thermodynamic on the base of thermodynamical rule first and second.In the end,economical values were used to evaluate in quantity,which can access feasibility and anti-risk ability of scheme.Firstly,thermal plant’s design working condition model was established with the following validation to the CoHP model(progress in all main devices’ model)and auxiliary devices’ math equilibrium was listed.Calculation methods of CoHP model’s efficiency with peak and valley time under transient working condition were shown under thermodynamic first and second rules.Net present value(NPV)and internal rate of return(IRR)was adopted to access feasibility and anti-risk ability of scheme.Screw turbine was used to recover steam’s throttling energy coming from intermediate turbine’s last stage to enlarge unit’s power generation under peak time,while turbine exhaust steam’s excess heat was fully recovered through a series of auxiliary devices to improve unit’s efficiency.Secondly,CoHP’s different working strategies were obtained with reference to power grid’s needing demand to thermal plant when models under variable strategies were also established.Sensitivity study to shaft power,heating load and peak-shaving capacity was finished.Nodes’ parameters through all models were optimized to make model more reasonable,acceptable and reliable,which can make benchmark model’s and CoHP model’s all feasible region obtained.Comparison was also conducted to evaluate progress.At last,research results show:CoHP can well solve the problem of uneven distribution of electricity and heat in the production process in the time domain.In the same time CoHP can improve unit’s efficiency,exergy efficiency and reduce coal consumption compared to benchmark model.Meanwhile unit energy efficiency can reach 103%,0-27.3%higher than that of bench model.Exergy efficiency is improved 2.86%～5.44%,while coal consumption can be 118.8 g/(kWh)～294.5 g/(kWh).In devices’ 15 years lifetime,net present value is 1.05 billion RMB,and payback period is about 1.6 year with internal rate of return is 49.8%.CoHP scheme have reliable feasibility and anti-risk ability during actual action.Once revenue can be obtained in the third year,CoHP will benefit thermal plant.This paper may be of interest for CoHP system’s energy-saving power generation and heating dispatching.