Experimental Study On Coproduction Of Belite Q-phase Cement Clinker In Pulverized Coal Combustion Boiler

While coal-fired power industry provides our society with clean electric power, the generation of jillion fly ash confronts us with pressure from deterioration of environment. Study on comprehensive utilization and realization of resource, reduction and benefit of fly ash become ways and means of mitigation of environment pressure and shortage of nature resource. The innovation of coproduction technology of cement clinker in PPC (pulverized coal combustion) boilers of power plants, lie in achievement of source utilization of fly ash , realization of circular economy between coal-fired power industry and cement industry and breakthrough of impasse of traditional utilization of fly ash.In order to select reasonable series and types of coproduction cement clinker in PPC boilers, based on status analyses of coproduction technology of cement clinker, comparison of raw material characteristics, calcinations condition, chemical composition,mineral component and hydration performance were carried out between different series of cement and clinker, and the properties and difference between minerals in coal ash and silicon -aluminum raw materials of cement were analyzed. Problem of coproduction of traditional cement were analyzed. Then,Q-phase with low alkalinity,low calcinations temperature and better hydration performance was introduced to coproduction technology of cement clinker. In this dissertation, the idea was originally put forward to cogenerate Q-phase cement clinker in PPC boilers, and the sort principle of coproduction of Q-phase cement clinker was primarily designed according to properties of coals.In order to ascertain formation mechanism of Q-phase in the process of cement clinker coproduction, experiments of transform of pure mineral of 2CaO·Al₂O₃·SiO₂ into Q phase were conducted on high-temperature box-type resistance furnace.Then,on the base of experiment results, high-sulphur Changguang coal and low-sulphur Yanzhou coal selected as experimental coals, experiments of mineral formation law of calcium-enriched modified fly ash were performed on two-stage polyphase reaction setup. The collected samples were analyzed by XRD, SEM and EDS,respectively. The results displayed that pure 2CaO·Al₂ O₃·SiO₂ with suitable content CaO and MgO could transform into Q phase; Wheather Changguang coal or Yanzhou coal, with adjustment of addtives content in agglomeration coal powder, minerals component of coproduction modified fly ash varied from mainly con sisting of no-active minerals gradually to appearance of trifling cement clinker minerals, to appearance of cement clinker and aim mineral of Q-phase. Experiments results testified the feasibility of coproduction of Q-phase cement clinker from high-sulphur Changguang coal and low-sulphur Yanzhou coal.High-sulphur Changguang coal as experimental coal, experiments of influencing factors such as calcinations temperature, material retention time, agglomeration coal powder preparation method and atmosphere in furnace on Q-phase cement clinker coproduction were performed on two-stage polyphase reaction setup. The results showed that under con dition of parameters of setup in this experiment, the best calcinations temperature was 1 3 30℃that was in accordance with temperature scope of pulverized coal combustion boilers; Under 1 330℃, at the range of 1.74 second to 6.94 second , extension of material retention time favored Q-phase cement clinker calcinations reaction; At a certain degree, the smaller particle of coal powder and calcium-base additive in agglomeration particles, the greater difference of sieving grade of coal powder and calcium-base additive in agglomeration particles, the easier solid reaction of CaO, MgO and minerals of coal powder took place in the process of combustion of agglomeration particle;Reducing atmosphere in furnace impact negative effect on formation of 3CaO·3Al₂O₃·CaSO₄, while formation of Q-phase can be promoted. With CaCO₃ replacing CaO,there was chance of formation of Q-phase.But increase of the ratio of none-combustible additives in agglomeration coal powder would give rise to heat value decrease,and the reaction of clinker minerals unsufficient. So further study on selection and addition technology of additive agent needs to do .With high-sulphur Changguang coal and low-sulphur Yanzhou coal selected as experimental coals, experiments of combustion characteristics and fusibility of agglomeration coal powder were investigated, The thermogravimetry results revealed that after adding calcium-based additives, the samples' curve of mass loss become gentle with the increasing ratio of additives in the samples;The velocity of mass loss curves' peak value fall, which showed the speed of loss weight went into slowly;the combustion process obviously sepa rated into two stages, and with the increasing of the ratio of additives, the burning intensity of the experiod was weakened gradually and in the anaphase the burning intensity was strengthened; the test sampler's ignition temperatures somewhat increased, the kindling retention time prolonged, and the stability of combustion decreased. With the additive ratio increasing, the inter mixture's convert ash ratio augmented, and the exotherm's width of peak get narrow, and the value of calorific power trailed off, and the time of burnout were postponed. The fusion characteristics expriment results showed that with addition of CaO gradually increasing from zero to certain degree, melting characteristics temperature of agglomeration coal powder present variation law of V type. Compared with original Changguang coal and Yanzhou coal, slagging tendency of agglomeration coal powder for coproduction of Q-phase cement clinker was mild. Thermal reaction of minerals of coal ash in pulverized coal combustion boilers were simulated in high-temperature box-type re sistance furnace. Mineral components of coal ash at soft temperature were analyzed by X-ray diffraction, and further theoretically analysis of variation mechanism of melting characteristics temperature of agglomeration coal powder was conducted making use of ternary phase diagram of CaO-Al₂O₃-SiO₂ system .The results showed that with content of CaO and MgO added into agglomeration coal powder varying, existence of co-melting com pound in mineral components of agglomeration coal powder ash gave rise to decreasing of melting characteristics temperature.Experiments of Q-phase cement clinker coproduction were conducted on two-stage polyphase reaction setup under optimized calcination condition. High-sulphur Changguang coal and low-sulphur Yanzhou coal selected as experimental coals, and the collected clinker samples were quantitatively analyzed by X-ray diffraction. The results showed that the minerals components of cement clinker mostly consisted of 2CaO·SiO₂ and Q-phase, and the content of 2CaO·SiO₂ of cement clinker accounted for 57.2% and 46%, and the content of Q-phase of cement clinker accounted for 27.2% and 32.1% . According to minerals components of cement clinker, dual performance of 2CaO·SiO₂ and Q-phase of cement clinker coproduction were fully taken into account. The sample can be named "belite-Q phase cement clinker". The properties of coproduction cement clinker from Changguang coal were tested at measurement laboratory of Zhejiang Zhuji Fuli Cement Co., Ltd. The results indicated that strength of compress and flexiblity of mortar samples at different ages were close to national standard of 32.5 grades Portland cement; when 30 percent Portland cement clinker was added to belite Q-phase cement clinker, strength of compress and flexiblity of mortar samples at different ages exceeded national standard of 32.5 grades Portland cement. Dry shrinkage, setting time and invariability of belite Q-phase cement clinker all satisfied involved national standard of cement clinker. Apart from 2CaO·SiO₂, 2CaO·Al₂O₃·8H₂O crystal, 3CaO·Al₂O₃·3CaSO₄·32H₂O, xCaO·SiO₂·yH₂O gel, and Al₂O₃·3H₂O gel appeared in 3d hydration sample. With hydration process developing, hydration product of 2Ca O·Al₂O₃·8H₂O, 3CaO·Al₂O₃CaSO₄·12H₂O, 3CaO·Al₂O₃·6H₂O gradually enriched.The content of sulfur and free CaO of coproduction cement clinker were measure ed.The results showed that when pulverized coal combustion boilers coproduced belite Q-phase cement clinker, desulfurization efficiency in furnace can be simultaneously enhanced; and the content of free CaO of coproduction cement clinker amounted about to 1 %, meet ing the national standard of cement clinker.Based on the assumption of spherical aggregation particle of agglomeration coal powder, process analysis of coproduction of belite Q-phase cement clinker was reduced to analysis of spherical aggregation particle ashing. Dehydration and decomposition reaction of minerals of coal under high temperature were analyzed, and the chemical composition of cement clinker coproduction from high-sulphur Changguang coal and low-sulphur Yanzhou coal were preliminary investigated. By means of empirical equation, thermo dynamic parameters of Q-phase were estimated. In the light of thermodynamic function of state Gibbs free enthalpy, the free enthalpy variation of mineral formation reactions taking placing in process of coproduction of belite Q-phase cement clinker from Changguang coal and Yanzhou coal were calculated, and the sequence of priority of mineral formation reactions were found out, and the resultants in process of coproduction of belite Q-phase cement clinker were investigated. The analysis conclusion accorded with experiment results of belite Q-phase cogeneration from Changguang coal and Yanzhou coal. Making use of Gentling equation, kinetics analyses of coproduction of belite Q-phase were carried out. Mineral formation chemical of beliet Q-phase cement clinker coproduction from Changguang coal andYanzhou coal were preliminary set up.Last but not least,the benifts of coal-fired power enterprise and cement enterprise were predicted by micro-case method ,one year as analytical period, one 1 004 (t.h^-1) PPC boiler for 330MW power set selected as analyzed object. The analyses showed direct profits of 66 580 000 yuan one year can be made for coal-fired power enterprise and cement enterprise. Cement enterprise can yearly save clay 76 600 t, cement mixture 86 200t. Energy consumption would yearly save 20 240t coal equi valent.