Research On The Technology And Equipment Of The Raw Gas Sensible-heat Recovery In Ascension Pipe Of Coke Oven

China is the largest coke supplier and consumer in the world.In 2018,China produced 438.0 million tons of coke,which accounted more than 70%of global production.The coking industry is not only an important energy production department,but also a large energy consumer.Coking accounted for about70%-80%of the total energy consumption in the coking process,in which heat loss results from raw gas accounts for 32%-36%.Sensible-heat recovering has been a research hot-spot in coking industries for a long time.However,raw gas sensible-heat hasn't been reasonably and effectively recovered due to the technical problems of“leakage”,“coking corrosion”and“graphite accumulation”in the process of raw gas sensible-heat recovery at present.In this work,coking mechanism for raw gas was revealed,anti-coking&non-stick coating combined with ascension pipe evaporator were developed,experimental system as well as demonstration project were constructed,thermal performance of ascension pipe evaporator combined with stability,reliability and rationality properties of anti-coking&non-stick coating were verified,all the above work achieved the goals of recovery and utilization of sensible-heat for raw gas,solving the problems of leakage and coking corrosion in coking industry.Firstly,formation and evolution mechanism of carbonaceous deposits on the surface of coking chambers was investigated.Based on the characterization of carbonaceous deposits,it could be found that:polycyclic aromatic hydrocarbons in raw gas formed metastable primary carbon particles with diameter of 3.0-5.0?m in coking process.Primary carbon particles further formed intermediate carbon particle with diameter of 0.5-2.0?m in high temperature.At last,ultimate carbonaceous deposits was formed.C content was increased with decrease of O and N content in the formation of carbonaceous deposits.The absorbed O₂and H₂O took part in the oxidation reaction of carbon skeleton to form=O and-O structure.The oxidation process combined with elimination reaction of oxygen-containing groups resulted in the change of bonding state of O element,finally formed carbonaceous deposits with high graphitization.Secondly,coke layer on the surface of ascension pipe was aimed to investigate coking mechanism for raw gas.It was found that:polycyclic aromatic hydrocarbons in raw gas formed porous structure with 0.1-1.0?m carbon particle loosely stacked.The diameter of carbon particles gradually increased to 1.0-3.0?m.The carbon particles presented gradually increased compactness with periodic change of coking temperature,which resulted in compact coke layer displayed lots of patterned structure.It was also found that:metal elements(especially Fe)presented strong catalytic action in coking corrosion process,promoting the elimination reaction of=O bond in the form of carbonyl,quinone and carboxylic acid(salt)combined with-O-bond in the form of esters,alcohols,phenols and ethers.Furthermore,inert oxide including Si O₂,Ti O₂,Mg O,Ca O and Al₂O₃were introduced to fabricate anti-coking&non-stick coating.Miniature coking system was constructed to comparatively investigate coking characteristics of coating and310s stainless steel sample by combining with material characterization technologies.It could be found that:Coatings presented smooth surface after high-temperature treatment,significantly inhibiting physical sagging of coal tar,and inert coating exited excellent shielding effect to active site on the surface of metal,eliminating catalytic coking effect of metal elements including Fe.Raman spectra was introduced to investigate graphitization degree of coke layer on the surface of coating and 310s stainless steel,which presented I_D/I_Gvalue of 2.61 and2.27,indicating lower graphitization degree of coke layer on the surface of coating.The above investigation effectively solved technical problems of“coking corrosion”,“graphite accumulation”and“leakage”for ascension pipe.Computational fluid dynamics(CFD)software was applied to establish 3D mathematical model for heat exchange effect of evaporator on ascension pipe.The effect of evaporator structure and water-flow velocity on heat exchange efficiency were investigated,enriching and developing experimental investigation.It could be found that heat exchange efficiency was improved with the increase of number of evaporator fin.It presented better heat exchange effect with fin angle(?)of 18 ^o.Heat exchange efficiency was increased with increase of water-flow velocity(u).The system presented evaporation power of 71.0 k W when u was 0.05 m/s.When u?0.1 m/s,the system presented evaporation power of 71.1 k W and nearly unchanged.Based on the above work,pilot test platform of sensible-heat recovering for raw gas was established,which had stably run for 3 months,preliminary verifying the feasibility of the system.And also,the effect of circulation ratio N on graphitization degree of raw gas and steam output in sensible-heat recovery process were investigated.In coking process,average temperature of outlet in different values were higher than 500?with average temperature difference of200-260?between inlet and outlet.With the increase of N value,the wall temperature of outlet for ascension pipe was gradually decreased.The temperature was lower than 450?for 6 h in last stage of coking process when N=11,in which coking was appeared on the bottom of ascension pipe.With the increase of N value,outlet temperature of raw gas was gradually decreased with small range.It presented steam production difference of 9.7%between N=13 and N=5,indicating sensible-heat recovery efficiency of raw gas was not significantly enhanced.It was suggested N value of 10 considering safety operation and sensible-heat recovery efficiency in engineering application.Based on the pilot test,6.0 m ascension pipe raw gas sensible-heat recovery and utilization demonstration project was built and superheated steam production scheme was designed.Unattended real-time on-line monitoring system was successfully developed and applied for the first time,in which operation condition of every evaporator could be monitored,realizing online diagnosis and early warning of leakage of evaporator.Since the project launched for 1 year,the system run stably without“leakage”and“coking corrosion”.The tar cleaning cycle or ascension pipe replacement cycle was increased from 2-3 months to more than 12months,significantly inhibiting graphite accumulation rate of raw gas in ascension pipe,thus effectively decreased daily cleaning workload and increased production efficiency.Compared with traditional technology,the recovery efficiency of this system was increased 30%with superheated steam production of 100 kg per ton of coke,realizing reasonable recycling of sensible heat for raw gas.