井下热力发生器燃烧仿真模拟

Analogue simulation of combustion in downhole thermal generators

井下热力发生技术原理为将热力发生设备集成后置于井下,向井下输送空气、燃料和水,基于高压燃烧喷射机理,燃料与空气在燃烧室中充分燃烧,依靠产生的高温高压烟气将混合掺入的水汽化,产生复合热流体注入地层。因井筒尺寸受限,相比地面多元热流体发生器,井下热力发生器需在外径缩小1倍的情况下,输出排量提升4倍。结构变化后,主要面临燃烧是否充分、换热是否有效、输出温度和排量是否满足设计要求等问题,针对以上问题,本文建立了井下热力发生器流动与传热仿真模型,得到发生器工作时的温度场和流场分布,结果表明,发生器内部燃烧较为充分,最高烟气温度约1600 K,出口烟气温度约1300 K,出水温度370 K,即水温升高近80 K,但随水流量的增大,出口烟气温度有所降低,且当水流量过大,如43.4 t/h时,烟气最高温度、出口烟气温度反而升高,内衬最高温度也略有升高,出水温度降低,出现了冷却性能下降的工作状况。

The principle of downhole thermal generation technology is to integrate the thermal generation equipment and place it downhole to transport air,fuel,and water.Based on the high-pressure combustion injection mechanism,the fuel and air are fully burned in the combustion chamber,and the mixed water is vaporized by the generated high-temperature and high-pressure flue gas,generating a composite thermal fluid and injecting it into the formation.Due to the limitation of wellbore size,compared with the surface multi-element thermal fluid generator,the output displacement of the downhole thermal generator needs to be increased by four times under the condition of reducing the outer diameter by one time.After the structural change,the main problems faced are whether the combustion is sufficient,whether the heat exchange is effective,and whether the output temperature and displacement meet the design requirements.In response to these problems,this paper establishes a simulation model for the flow and heat transfer of an downhole thermal generator,and obtains the temperature and flow field distribution of the generator during operation.The results show that the internal combustion of the generator is relatively complete,with a maximum flue gas temperature of about 1600 K,an outlet flue gas temperature of about 1300 K,and an outlet temperature of 370 K,the water temperature rises by nearly 80 K,but with the increase of water flow rate,the outlet temperature of the flue gas decreases.Moreover,when the water flow rate is too high,such as 43.4 t/h,the highest temperature of the flue gas and the outlet flue gas temperature actually increase.The highest temperature of the lining also slightly increases,and the outlet temperature decreases,resulting in a decrease in cooling performance.