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Furnace gas waste heat recovery and energy saving effect analysis
Author：sehenstar Source：SeHenStar Pubtime：2014-10-08 10:20:20 Click：1242
Waste heat and energy technology is the most important resource comprehensive utilization technology, forconserving resources, improving the State of the environment, enhance economic efficiency, achieve optimalallocation of resources and sustainable development is of great significance, in which iron and steelenterprises furnace waste heat recovery technology research attracted the attention of industry in recent years. 2011 Guiyang steel mills on consteel electric arc furnace gas waste heat recovery system of thesuccess.
A steel plant furnace put into operation in 2000, and in 2005 after the process of transformation, intothe furnace hot metal ratio improved from last 15% to around 90%, furnace capacity by 600,000 t increasedto 1.1 million t per year. Electric furnace smelting and steel at the same time, produced approximately200000m3/h electric furnace high temperature gas from carrying large amounts of waste heat. Except few flue gas heat through Preheat waste steel of way get using outside, still has 350~800℃ of flue gas after burning settlement room Hou, through directly water-cooled way for cooling, will flue gas temperature dropped 300 ℃ following; cooling Hou of flue gas and from roof big cover of cryogenic flue gas mixed, makes flue gas temperature continues to down 180 ℃ following; while in into high temperature bag Duster Qian segment of flue gas duct Shang has accident mixed wind valve, in flue gas Super temperature Shi timely opened continues to reduced flue gas temperature, To protect the safe operation of the bag. Meetthe temperature requirement finally entered the after bag filter in purification of flue gas fan into thechimney. Furnace flue gas cooling method not only led to a large number of furnace gas waste heat waste ofresources, and added cooling system power consumption, leading to energy waste.
In addition, domestic iron and steel enterprises in order to further reduce the cost of electric furnacesteelmaking, smelting electric furnace process prevailed against molten iron scrap steel models and hot metal ratio can be as high as 70%, electric equipment "converter" trend. As the electric stove furnace hot metal ratio increases, the flue gas temperature, flow and amount of dust is originally designed load haschanged a lot, the original dust removal system, even at full capacity overload, increase theenvironmental discharge problems.
1, technical improvement scheme analysis
1.1 problem analysis
Characteristics of electric arc furnace production process determines the flue gas temperature and flowhas a large cycle fluctuation, while electric arc furnace dust from flue gas waste heat recovery equipmentlayout and structural characteristics on the subsequent form requirements are very high. While oxygenblowing smoke during smelting of flow, temperature, flue gas to heat exchange tube of waste heat boiler of the thermal shock and abrasion erosion most structures must adapt to fluctuations due to flue gas ofboiler the thermal stress effects. Flow minimum tapping during the flue gas temperature is low, on theother hand, flue gas velocity decreased, the boiler heating surface fouling tendency more and moreserious, affecting the next cycle of steelmaking boiler heat, exhaust gas temperature will rise graduallyand thereby affect subsequent operation of dust collection equipment. Targeted design and type selectionof boiler is particularly important.
Meanwhile, electric furnace smelting conditions and initial design conditions change dramatically, smoke,dust and flue gas temperature and the design parameters are very different, this need for analysis ofparameters related to theoretical analysis and test validation.
1.2 the main technical program
According to the features of electric resistance of the placing of the flue gas system, site spaces siteand comprehensive considerations such as ash, after repeated design, ultimately choose to adopt combinedconvective heat transfer and settlement of radiation cooling and dedusting technology, major equipmentincluding water settling Chamber, evaporator at low temperature, in high temperature evaporator,superheater and economizer, heaters and related systems.
(1) flue gas heat recovery system settings
Exports in the first two combustion chamber design a set irradiation of water wall in the front gradually settled, and follow-up after a 90 ° angle in the original pipeline underneath a set of convective heattransfer of flue gas. In first group heated surface in the used radiation water-cooled wall component can will through II burning room out of high temperature flue gas of temperature for preliminary integration, while reduced flue gas velocity to completed flue gas in the big of dust particles of preliminary settlement, to reduce follow-up boiler and dust device of load, while will flue gas in the not full burning of gas in settlement room continues to reaction burning completely, to avoid to follow-up equipment or device brings explosion damage effects, up to on high temperature flue gas cut peak of role.
Flue gas through the water after settling into waste heat boilers, waste heat boiler under fieldconditions, using horizontal layout, followed by high temperature flue gas at high temperatures in theevaporator, superheater and low temperature evaporator and economizer, heat exchangers (low-temperaturedew point corrosion resistance), and finally discharge followed by purification of flue gas back into theatmosphere.
(2) the vapor recovery system with accumulator
Due to the electric furnace for periodic discontinuous blowing, so the addition of 2 accumulators in steamsystems, its role is the cyclical fluctuations of the waste heat boiler steam, by regulating the heat accumulator, to external steam supply continuously and steadily, to maximize recovery and utilization ofsteam.
By saturated steam waste heat boiler can generate 1 Chang 6 MPa, after the heat accumulator supply 1 free1MPa saturation steam back to the boiler's superheater achieve stable output, steam upon overheating, can be reached 260~350℃ and into the steam network.
Energy saving effect analysis for 2,
(1) waste heat recovery efficiency analysis
Furnace flue gases calculated at 200000m3/h, 500 ℃ checked via a waste heat boiler, can be recycled onaverage 1 Cheong 0MPa, 250 ℃ steam 25t/h, annual recycle about 200,000 t, saving about 250 ℃ steam25t/h, annual recycle about 200,000 t, energy saving 20,000 TCE, can provide considerable economic benefits creation of enterprises.
(2) reduced legacy cooling system energy consumption
Additional flue gas waste heat recovery heat recovery devices, you can deactivate the original water cooled, making smoke temperature of the flue gas temperature is reduced to a reasonable after emptying,reduces the consumption of cooling water.
(3) lower flue systems flue gas disposal amount of waste heat boiler flue gas temperature can be reducedto below 200 ℃, making subsequent introduction of mixed air flow from the roof liner is also reduced,need to deal with a corresponding reduction in the amount of flue gas dust-removal system.
3, conclusion
(1) the reconstruction scheme of heat recovery technology is feasible, reasonable system design.
(2) after the transformation can significantly reduce operating costs, lower energy consumption, bycalculating the transformation of unit energy consumption of per ton steel furnace can drop 18.32kgce,could save 20,000 TCE annually after the transformation is complete.
(3) the modification could solve the electric furnace dust removal to meet state environmental protectionrequirements.
(4) in recycling waste heat to produce steam used in production, instead of part of gas boiler producessteam, cut steel CO2, SO2, NOx emissions, energy-saving and emission reduction objective.
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