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热法磷酸特种反应塔底部余热回收的技术研究

作者:润色论文网  来源:www.runselw.com  发布时间:2019/10/26 14:23:12  

摘要:在传统热法磷酸生产中,黄磷燃烧释放的反应热并没有得到利用,反而需要燃煤锅炉提供蒸汽来进行熔磷和设备保温,尤其是热法磷酸特种反应塔(以下简称为反应塔)的底部,即下封头到下配水环形管所对应的平行面之间,并没有任何余热利用。这是高温燃烧区,对冷却要求较高,不能出现烧穿,鼓包等现象,一直是余热利用的难点。目前反应塔底部是采用夹套式的低温水冷却方式来确保安全运行,底部热量约占整个反应塔的15%。

本文首先建立反应塔底部结构模型,模拟燃烧过程,根据热平衡原理绘制底部能流图,进一步得出热平衡关系式,计算底部燃烧反应热力参数。紧接就反应塔底部燃烧情况分析热损失原因,重点提出了两种改进方案:在热法磷酸特种反应塔的基础上,新增了底部余热回收结构,采用强制循环方式进行独立辐射换热;另一种是同样的布置方式,采用自然循环方式进行辐射换热。

在底部余热回收设计中,重点需解决三个问题:在底部倒锥形内壁面上水冷壁管的选型及布置方式;两种水循环方式的选择及安全校核;两种底部余热回收方案的可行性及经济性分析。

本文在初步提出底部余热回收设计方案后,即针对上述三个重点问题进行展开。根据先前底部燃烧热力参数,将底部分为集箱和水冷壁受热面两个方面进行布置,同时对辐射受热管束的管型组合加以讨论,推导底部辐射换热系数与管型选择的关系式,得出最优的管型布置方式。

接着,对两种反应塔底部余热回收结构进行水循环校核,对于独立强制循环系统,在原工程经验的循环倍率取值范围内进行计算,得出几组相对应的循环倍率与循环泵功率的数据,通过Origin拟合出二次曲线,扩大了循环倍率的经验取值区间,根据反应塔的生产规格,确定出最经济安全的选值;对于自然循环,主要保证汽水流动,不在管中产生堆积,同时验证两种循环方式的可靠性。

最后,通过实例计算,结合风险因素,从投资与回报角度,分析底部余热回收的可行性。

In the traditional device producedphosphoric acid by thermal process, the reaction heat released by thecombustion of yellow phosphorus has not been utilized. Instead, coal-firedboilers are required to provide steam for phosphorus fusing and equipmentinsulation. Especially the bottom of the special reaction tower producedphosphoric acid by thermal process (hereinafter referred to as the reactiontower), that is, between the parallel faces of the lower head and the lowerwater distribution ring pipe, and there is no utilization of waste heat. Thisis a high-temperature combustion zone, which requires high cooling standard,can not appear burnt through, bulging, etc., has always been a difficult pointof waste heat utilization. At present, the bottom of the reaction tower adoptsjacketed low-temperature water cooling to ensure safe operation. Aftercalculation, the heat at the bottom accounts for about 15% of the entire reactiontower.

In this paper, the structure model of thebottom of the reaction tower is first established, the combustion process issimulated, the bottom energy flow diagram is drawn according to the principleof heat balance, and the thermal equilibrium relationship is further obtained,and the thermal parameters of the bottom combustion reaction are calculated.Then analyze the heat loss at the bottom of the reaction tower according tocombustion situation, and propose two improvement schemes. On the basis of thespecial reaction tower produced phosphoric acid by thermal process, a new wasteheat recovery structure is added, which adopts forced circulation to exchangeradiant heat. Another is the same arrangement, using natural circulation forradiation heat transfer.

In the structural design of the waste heatrecovery at the bottom, there are three problems that need to be solved: theselection and arrangement of water wall tubes on the bottom inner wall ofinverted cone; choice of two water circulation methods and safety check;feasibility and economic comparison of bottom waste heat recovery schemes.

After the preliminary design of the bottomwaste heat recovery structure, this article expands on the above three issues.According to the previous bottom combustion thermal parameters, the bottom isdivided into two parts: the header and the water-cooled wall heating surface.At the same time, the tube type combination of the radiation-heated tube bundleis discussed, and the relationship between the bottom radiation heat transfercoefficient and the tube type selection is derived to obtain the optimal tubetype arrangement.

Then, the water recycling check isperformed on the waste heat recovery structure at the bottom of the reactiontower. For the independent forced circulation system, the calculation iscarried out within the range of the cycle rate of the original engineeringexperience, and the data of the corresponding cycle rate and circulation pumppower are obtained. The quadratic curve is fitted by Origin to expand the cyclerate. According to the production specifications of the reaction tower, themost economical and safe selection of the cycle rate is determined. For thenatural circulation, it is mainly ensured that the flow of steam and water doesnot accumulate in the pipe. Simultaneously verify the reliability of the twocyclic modes.

Finally, through the calculation ofexamples, combined with risk factors, the feasibility of bottom waste heatrecovery is analyzed from the perspective of investment and return.

关键词:热法磷酸;余热回收;能量平衡;优化设计;水循环校核

thermal production of phosphoric acid; waste heat recovery; energy balance;optimized design;water cycle check

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