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天然气水合物抑制剂甲醇回收设备中结垢机理及对策研究

作者:优质期刊论文发表网  来源:www.yzqkw.com  发布时间:2019/10/26 14:14:56  

摘要:针对目前天然气开采过程中,常伴有天然气水合物生成的情况。气田采用甲醇作为天然气抑制剂来防止天然气水合物的生成。在对甲醇进行回收过程中,由于含醇污水成分较为复杂常常导致设备的结垢,严重影响重沸器和换热器的工作效率。

针对甲醇回收设备中的结垢问题,根据热力学理论、流体力学理论以及结晶动力学理论对结垢机理进行了分析和探究。在实验室内展开了碳酸钙结垢规律研究实验和除垢剂性能分析以及复配实验,研究了结垢的机理和除垢措施。为天然气抑制剂甲醇回收过程中造成的结垢现象和日后除垢防垢提供了一定的理论基础。主要的研究内容和结果为:

(1)分析了甲醇回收装置,并采集了设备里的含醇污水以及垢样进行组分分析。采用多功能离子色谱仪对水样中的成垢阴阳离子进行定性及定量检测分析。实验发现,水样含有较高浓度的Ca2+、Mg2+、Ba2+、Sr2+、Fe2+等成垢金属阳离子和SO42-、HCO3-等成垢阴离子,同时伴有K+、Na+、Cl-等离子混合存在,水质成分较为复杂,且矿化度高。水样呈弱酸性,具有较强的结垢趋势。

采用扫描电镜(SEM)、滴酸试验和高温失重法等对采集垢样进行形貌形态观测和成分组分分析。实验结果表明甲醇回收设备中的垢样92%为碳酸钙垢物,且其晶体形态主要为方解石结构,具有致密稳定且难以清除的特点。

(2)对甲醇回收装置中的结垢进行了化学反应机理分析以及结晶动力学机理分析:甲醇回收装置中的结垢过程是不配伍离子间相互混合以及热力学条件的变化还有固体吸附共同作用的结果。其过程可以表示为水溶液→溶解度降低→过饱和溶液→晶体析出→晶体长大→结垢。这一过程不光受含醇污水中各种离子的溶解度以及在水中的过饱和度影响,还与化学反应、结晶动力学以及热力学等多种因素相关。

此外还进行了水溶液结垢影响因素分析。水溶液中成垢离子的浓度、压力、温度、pH值以及矿化度等因素都会对装置的结垢产生影响。成垢离子浓度越高,对结垢的影响越大;由于垢体主要为碳酸钙,随着温度的升高结垢趋势愈加明显,高矿化度和弱酸性水质在一定程度上减弱了结垢的趋势。

(3)研究碳酸钙的结垢规律,在实验室内展开了静态滴定实验、电导率法探究碳酸钙结垢规律实验、反应速率求解和活化能求解。根据实验分析可知温度升高,碳酸钙的结垢趋势增强,在30℃-90℃温度范围内,结垢量与结垢率增加,电导率下降;成垢离子浓度增加,结垢量与结垢率升高,电导率下降。同时盐含量也对结垢量有所影响,当NaCl浓度小于40g/L时,结垢量与结垢率均下降,电导率上升,结垢趋势减弱。晶核生长的反应速率要远大于晶粒长大的反应速率且晶核生长过程相比晶粒长大过程受温度变化的影响更大。晶核生长以及晶粒长大所需的活化能分别为46.56KJ•mol-1和497.13KJ•mol-1,晶核生长过程相比晶粒长大过程所需要的活化能更小。

(4)以实验为基础,探究防垢除垢措施。分析了目前常用的几种除垢方法,最终选取了化学除垢法作为主要研究对象。根据化学除垢剂的基本特征,初选了8种除垢剂进行了性能分析实验,分别从pH值、温度适应性、Ca2+浓度影响以及HCO3-浓度影响四个方面对待选的除垢剂进行实验,根据实验结果筛选出表现最佳的三种除垢剂,分别是PAA、HPMA和MA-AA。对本次选取的三种除垢剂进行复配实验,直接作用于甲醇回收设备水样。为了选取除垢效果最佳的复配配方,分别对三种除垢剂进行了1:1、1:2、2:1、2:3、3:2、1:3和3:1多种比例进行复配,设置复配浓度为4-14mg/L。复配结果表明PAA与HPMA以3:2的比例10mg/L浓度进行复配时,除垢率高达89.3%;PAA与MA-AA以3:2的比例10mg/L浓度进行复配时,除垢率高达89.6%;HPMA与MA-AA以2:1的比例12mg/L浓度进行复配时,除垢率高达91.4%。

In the current natural gas exploitationprocess, it is often accompanied by the formation of natural gas hydrates. Agas field uses methanol as a natural gas inhibitor to prevent the formation ofnatural gas hydrates. In the process of recovering methanol, the fouling of thealcohol-containing sewage often leads to the scaling of the equipment, whichseriously affects the working efficiency of the reboiler and the heatexchanger, and poses a serious threat to the safety of the methanol recovery operation.

In this paper, the fouling mechanism ofmethanol recovery equipment is analyzed and explored according to thermodynamictheory, fluid mechanics theory and crystallization kinetics theory. In thelaboratory, the research progress of calcium carbonate scaling and theperformance analysis of descaling agents and compounding experiments werecarried out, and the mechanism of scaling and descaling measures were studied.It provides a theoretical basis for the fouling phenomenon caused by thenatural gas inhibitor methanol recovery process and the future descaling andanti-scaling. The main research contents and results are as follows:

(1) Investigated a methanol recovery unitin a gas field in Changqing, and collected alcohol-containing sewage and scalesamples from the equipment for component analysis. Qualitative and quantitativedetection and analysis of scaled anions and cations in water samples bymulti-function ion chromatography. It was found that the water samplescontained higher concentrations of scale-forming metal cations such as Ca2+,Mg2+, Ba2+, Sr2+, and Fe2+, and scale anions such as SO42- and HCO3-,accompanied by K+, Na+, and Cl- plasmas. It is more complicated and has a highdegree of mineralization. The water sample is weakly acidic and has a strongtendency to scale.

(2) The chemical reaction mechanismanalysis and crystallization kinetic mechanism analysis of the scale in themethanol recovery unit are analyzed. The analysis shows that the foulingprocess in the methanol recovery unit is incompatible with the intermixing ofions and the change of thermodynamic conditions. Complex results of solidadsorption interactions. The process can be expressed as aqueous solution →reduced solubility → supersaturated solution → crystal precipitation → crystalgrowth → scaling. This process is not only affected by the solubility ofvarious ions in alcohol-containing sewage and supersaturation in water, butalso related to various factors such as chemical reaction, crystallizationkinetics and thermodynamics.

In addition, the factors affecting thescaling of aqueous solutions were also analyzed. Factors such as concentration,pressure, temperature, pH, and salinity of the scaled ions in the aqueoussolution can affect the fouling of the device. The higher the scale ionconcentration, the greater the influence on the scale; Since the scale ismainly calcium carbonate, the scaling tendency becomes more and more obviouswith the increase of temperature. The high salinity and weak acid water qualityweaken the tendency of scaling to some extent.

(3)Exploring thescaling rule of calcium carbonate, static titration experiment and conductivitymethod were carried out in the laboratory to explore the calcium carbonatescaling rule experiment, reaction rate solution and activation energy solution.According to the experimental analysis, it is known that the temperature rises,the scaling tendency of calcium carbonate increases, the fouling amount and thefouling rate increase, and the electrical conductivity decreases; the scale ionconcentration increases, the fouling amount and the fouling rate increase, andthe electrical conductivity decreases. At the same time, the salt content alsohas an effect on the amount of fouling. In the system with large salt content,the amount of fouling and fouling rate decrease, the conductivity increases,and the fouling tendency decreases.

关键词:甲醇回收设备;结垢机理;结垢规律;反应速率常数;除垢措施

methanol recovery equipment;fouling mechanism;fouling law;reaction rate constant;descaling measure

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