Study Of Direct Hydrogen Production From Carbonaceous Fuels

The conventional utilization of carbonaceous fuels brings about heavy local pollution(particulate matters,SO₂ and NOx)and CO₂ emission.The universal concern on global climate change caused by CO₂ emission will greatly influence the development of China in terms of energy system.Hydrogen energy is getting more and more globally attractive for its cleanness,effectiveness and flexibility in applications.It is expected to be one of the end-use energy carriers in the future. Hydrogen is secondary energy,and needs to be produced from primary energy resources.Hydrogen production from carbonaceous energy with reducing the amount of pollution and CO₂ is most likely to be carried out in the future.According to concept of 'direct hydrogen production with CO₂ sequestration by mineral',basing on the data from constant volume experiments,this work set up a constant pressure experimental facility.On this facility,studies of the effect of temperature,pressure,Ca/C ratio on the hydrogen production reaction with reactants continuous supplied had been carried out.1.On the base of constant volume experiments,verification test were carried out on an autoclave.The effect of temperature,Ca/C ratio,coal ash on the reaction on the reaction had been explored,and the suitable operating conditions of direct hydrogen production were determined primarily,then the results can be used as the found of designing the continuous experimental facility.2.According to the results of constant volume experiments,the main parameters of the direct hydrogen production system and the characteristics size of reactor were established.And then,according to these parameters,detailed design of all kinds of equipments was made,including:the main reactor,the dry powder feeding system, the steam generator,gas-solid separator and gas-liquid separator,etc.On the base of constant volume experiments,a continuous experimental facility had been build up. The problem had been solved include:the reactor working on high pressure and high temperature,the quantitative supply of reactants,the supply of dry powders into the pressured reactor and the separation of products.A method of operation of the continuous facility has been summed up,and the platform of direct hydrogen production had been build up.3.A fixed bed method was used to study the gas products at the present of steam during the elevated temperature.The results showed that under a certain pressure, there exists a sensitive temperature:lower than this temperature,the rate of reaction is slow and the yield of hydrogen was small;above this temperature,the yield of hydrogen is much more.Hydrogen yield raised rapidly when the temperature is above 650℃under the pressure of 3MPa.4.By the method of spouted bed,a continuous direct hydrogen production process was realized with solid reactants and steam continuously supplied into the pressured reactor.A bituminous coal(XinZhou coal)was used as parent material. Experiments on the effect of Ca/C ratio,temperature,pressure on the reaction were carried out.a)Under 3MPa,the experiments on different Ca/C ratio showed that the hydrogen yield was large when Ca/C was 1.0,and at lower Ca/C ratio the hydrogen yield was small with lower H₂/CH₄;while,when the Ca/C ratio was 1.5,the hydrogen yield was not large as expected, which is mainly thought to be the reason of solid melting.b)The study on the effect of temperature showed that the gas yield increased with the elevation of temperature.The hydrogen yield increased with the rising of temperature from 600℃to 700℃,while,at higher temperature reaction condition such as 800℃,the content of hydrogen decreased with a increasing content of carbon dioxide.This is the result of inhibiting of the carbon dioxide absorption reaction at high temperature.The content of methane decreased with the elevation of temperature. c)The results of experiments on the effect of different pressure showed that higher pressure was suitable for direct hydrogen production.d)H₂S and NH₃ were detected in the product gas.The content of H₂S was only 5ppm content in the product gas at representative conditions,and increased with the elevation of temperature and pressure.The content of NH₃ increased with the elevation of temperature and pressure.The parameters such as temperature,pressure and the Ca/C ratio affected the characteristics of solid melting,and must be considered when designing the operation conditions.