Research On The Multi-period Optimal Scheduling Model Of Byproduct Gas System In Steel Plants

Increasing the utilization efficiency and reducing the energy purchasing cost are the key focuses of the energy management in steel enterprises.Byproduct gases are important secondary energy sources generated in steel making process,and 33%of coal energy is converted into byproduct gases.Therefore,the comprehensive utilization of byproduct gases is significant for energy saving and emission reduction in steel industry.Under this background,this paper focused on the byproduct gas system and proposed several optimal scheduling models applied in three typical steel enterprises in China.The purpose is to reduce the energy consumption and production cost.The main results are as follows:(1)The analysis on byproduct gas system in steel enterprises demonstrated that the production amount of three kinds of byproduct gases not only related to the quality of raw materials for iron and steel making,but also related to the operation of metallurgical equipment and processes.On the other hand,the consumption of byproduct gases is influenced by the operation,process demand and the equipment level.When time-of-use power price is not considered,the most important thing is to sustain the stability of gasholder system.But if the time-of-use power price is considered,the stability as well as electricity benefits from peak load shifting should be simultaneously taken into account,which requires higher level for gasholder operation.(2)The penalty factors are a group of key variables in the scheduling model.The purpose is to realize the conversion between sub-objective functions,and the influence of penalty factors on the optimization results cannot be ignored.When the gasholder common penalty factor x increases or the boiler common penalty factor y decreases,the stability of gasholders are improved and the stability of boilers are reduced.We proposed an effective method to select reasonable combination of penalty factors.The case study conducted on H steel plant demonstrated that the best combination of penalty factors located in an enclosed area,which is narrow and long.The enclosed area begins at x=0.231.y=621.9 and ends at x=0.274,y=797.4.Finally.the center of gravity for this enclosed area was regarded as the point for reasonable penalty factors.which is x?0.254,y=717.8.The stability of byproduct gas system in H steel plant is improved with the gasholder penalty cost and boiler penalty cost reduced by 21.8%and 66.2%.respectively.The sensitivity analysis results indicated that if the electricity price increased to 200%of current price.The gasholder level will gradually decrease and release more byproduct gases,and the total power generation will increase by 20%.(3)Based on the above,the influence time-of-use power price on the selection of penalty factors were discussed.The case study conducted on H steel plant demonstrated that the best gasholder common penalty factor x=0.002 with the corresponding standard deviation volume(SSDV)=20736 m3 and electricity purchasing cost(EPC)=290607.The overall operation efficiency of five boilers after optimization is 83.03%which is 3.3%higher than the manual operation.The power purchasing cost was decreased by 29.7%after optimization with the deviation of gasholder reduced by 62.0%.Sensitivity analysis result demonstrated that the peak-valley ratio(PVR)of electricity price can affect the optimization results.When the PVR increased to 200%of current value,the percentage of electricity generation(PEG)for the peak price period(PPP)increases from 40.27%to 42.8%,whereas those for the moderate price period(MPP)and valley price period(VPP)decreases from 33.45%to 31.15%and from 26.28%to 26.05%,respectively.Thus,increasing the PVR contributes to the peak-valley shifting of the electricity generation.Meanwhile,the SSDV gradually increases from 20,736 m3 to 28,443 m3,implying a decrease in the overall stability of the gasholder.(4)The actual operation data of on-site power plant in X steel plant during 2013 to 2015 demonstrated that the thermal efficiency of boiler can be reduced by 20%to 40%if the operation load of boiler decreased from 100%to 30%.Besides,if the on-site power plant has both boiler and CCPPs,the priority of gas supply is given to the CCPP,and the rest of gases are distributed to boilers according to their efficiency performance.The scheduling model always tends to increase the overall efficiency of the on-site power plant.The analysis on the load shiftingpotential in different types of steel plants indicates that the proposed model can decrease the electricity purchasing cost by 20?30%,which has a significant economic benefit.Finally.the study can provide theoretical support for the realization of efficient and intelligent management of the byproduct gas system.