Simulation And Analysis Of Sewage Sludge Gasification And Power Generation Systems Based On Aspen Plus

With the acceleration of urbanization and the increase of municipal sewage treatment rate,the sludge produced in the process of sewage treatment has also increased sharply.It is very important to treat and dispose of municipal sludge in terms of volume reduction,harmlessness,stabilization and resource utilization.Sludge gasification and power generation technology is a reasonable,efficient and clean sludge treatment process.Compared with other sludge treatment processes,gasification treatment has obvious capacity reduction effect,less harmful substances discharge and easy to control.Gasification produces combustible gas for power generation,and waste heat is further used for sludge pre-drying,which has high energy efficiency.Based on Aspen Plus simulation platform,the characteristics of sludge gasification at medium and low temperatures are studied firstly.On this basis,the sludge gasification and gas turbine power generation system and the sludge gasification and steam turbine power generation system are established.The combination of sludge gasification and the subsequent power generation of gas is analyzed and studied,which provides a certain reference value for the industrial design of sludge gasification and power generation system.Firstly,a fluidized bed experimental device was set up,on which the air gasification experiments of sludge at low temperature?600-850??were carried out,and the experimental data under different working conditions were obtained.Based on Aspen Plus platform,sludge gasification model was established,and four typical working conditions were selected to simulate,and the simulation results were obtained.The accuracy of the model is verified by analyzing the error between the experimental results and the simulation results.Based on the validated gasification model,the effects of air equivalent ratio,gasification pressure,sludge moisture content and dry-base calorific value of sludge on gasification characteristics were analyzed.The results show that the air equivalent ratio has a greater influence on the gasification process in the self-sustaining gasifier.With the increase of air equivalence ratio,CO,CO₂,CH₄ content in the gas shows a downward trend,while H₂content first increases and then decreases.Gas yield and gasification temperature showed an upward trend,while gas calorific value and cold gas efficiency showed a downward trend.When sludge gasification is carried out,the air equivalent ratio should be about 0.3.At this time,the gasification temperature is at a higher level,while the efficiency of cold gas does not decrease significantly.Gasification pressure has little effect on gas component volume fraction,gas calorific value,gas yield and cold gas efficiency,but increasing gasification pressure can significantly increase gasification temperature.When the gasification temperature is at the medium and low temperature level,atmospheric gasification is enough.The gasification pressure can be increased appropriately if the gasification process is matched with the subsequent utilization of the gas production.The sludge water content has a great influence on CO and CO₂ content in the gas,but has a little influence on CH₄ and H₂ content.Gas yield,calorific value and gasification temperature all decrease with the increase of sludge moisture content,while cold gas efficiency first increases and then decreases.When sludge is gasified,the moisture content should not be more than 15%.The higher the dry-base calorific value of sludge,the better the gasification process.With the increase of dry-base calorific value of sludge,gas yield,gas calorific value and cold gas efficiency all showed an upward trend.Secondly,the sludge gasification and gas turbine power generation scheme and the sludge gasification and steam turbine power generation scheme were designed,which combined the sludge gasification and the subsequent utilization of gas.The recovery and utilization of waste heat should be fully considered in the scheme design.In view of the sludge gasification and gas turbine power generation scheme,the heat of the high temperature exhaust is recovered to generate steam,and the sludge is dehydrated by steam.In view of the sludge gasification and steam turbine power generation scheme,the sludge is dehydrated by low-pressure steam extraction of steam turbine,which greatly reduces the cold source loss of condenser.Based on Aspen Plus,the system models of the two schemes are established,and the appropriate input parameters are selected to simulate the system.The thermal parameters of each logistics unit in the system are obtained,and the net power supply efficiency of the system is selected to evaluate the thermal performance of the system.For sludge gasification and gas turbine power generation system,the effects of water content of deep dewatered sludge,water content of hot-dried sludge and purification methods on the thermal performance of the system were studied.For sludge gasification steam and turbine power generation system,the effects of water content of deep dewatered sludge and hot-dried sludge on the thermal performance of the system were studied.The results show that the waste heat recovery is fully considered and cascade utilization of energy is realized in the two systems,so the energy utilization efficiency of the two systems is high.Among them,the net power supply efficiency of sludge gasification and gas turbine power generation system is 41.13%,and that of sludge gasification and steam turbine power generation system is 29.52%.In both systems,the net power supply efficiency increases with the increase of water content in deep dewatered sludge and decreases with the increase of water content in hot-dried sludge.In addition,for sludge gasification and gas turbine power generation system,the net power supply efficiency of the system is increased by 1.11%by high temperature purification.