地热流体开发利用中防垢除垢技术研究进展

地热流体结垢是阻碍地热资源稳定、经济和高效开发利用的因素之一。系统总结了中高温地热流体开发利用中防垢除垢技术研究进展。中高温地热田中代表性垢物是钙垢和硅垢,其中钙垢成分以CaCO₃为主,多形成于因压力下降导致CO₂脱气的开采井或者地面设备,硅垢成分以无定型SiO₂为主,多形成于因温度下降导致的溶解度减小的回灌井或者地面设备。实际生产中防垢除垢技术应结合地热流体利用方式进行选择和优化,直接利用方式可考虑采用基于CaCO₃和无定型SiO₂热力学性质的防垢技术;发电方式中钙垢可考虑阻垢剂注入的防垢技术,而硅垢则考虑利用石英和无定型SiO₂溶解度差异、调控温度、pH、无定型Si O₂浓度等防垢技术。     

南蒸馏—减粘装置节能优化组合改造

锦西石化分公司南蒸馏—减粘装置优化组合改造是一项重大的节能措施 ,该项目对减粘装置进行搬迁改造 ,与南蒸馏装置形成联合装置。通过合理规划减底渣油物料流向 ,减少中间过程能量损失 ,同时降低了两套装置的能耗     

超声波防垢除垢装置在热媒／原油换热器中的应用

介绍超声波防垢除垢技术的特点及其工作机理,阐述该超声波脉冲防垢除垢装置在原油长输管道系统中的实际应用情况和监测数据,并对其进行了经济分析和效果评价。实践证明,该装置使用5个月后,热夥原油换热器的换热效率提高了6％左右。     

渣油深度转化提高轻油收率技术的重大进展

目前全球炼油厂工业应用的渣油深度转化技术主要有两种:一是焦化,二是沸腾床加氢裂化。焦化技术最大的问题是把一部分渣油原料变成了石油焦和少量气体;而沸腾床加氢裂化技术的渣油转化率也只有55%～75%,渣油仍未得到高效利用,且装置投资大,操作复杂。所幸的是,现在渣油深度转化提高轻油收率技术有了新进展。沸腾床加氢裂化集成技术——LC-MAX工艺和H-Oil-延迟焦化集成工艺已经开发成功,正在准备工业应用,其中LC-MAX工艺渣油转化率可达80%～90%,并且提高了加工原料的灵活性,降低了反应系统的投资和操作费用。另外,渣油悬浮床加氢裂化技术也取得了突破性进展,正在建设工业装置的有KBR公司的VCC技术、UOP公司的Uniflex技术、Eni公司的EST技术和委内瑞拉国家石油公司的HDHPLUS技术。VCC技术的渣油转化率可达95%;Uniflex技术采用纳米级催化剂,转化率可达90%以上;而EST技术首套工业装置将加工难以转化的乌拉尔原油减压渣油,如果渣油转化率能达到95%,且能长期运转,将是渣油深度转化技术的重大突破。渣油悬浮床加氢裂化技术是当今炼油工业的世界级难题和前沿技术,国家"十二五"规划要求炼油行业到2015年轻油收率从目前的75%左右提高到80%。为此,建议抓紧组织产学研三结合的研发团队,充分发挥国家重点实验室和国家工程研究中心的作用,高度重视渣油悬浮床加氢裂化催化剂的筛选工作。同时,国家有关部门要加大支持和协调力度,确保到2015年取得重大突破。     

浆态床渣油加氢装置生产运行的分析和对策

为了实现原油最大化利用,原油中重质馏分(特别是渣油)的高效加工利用至关重要。目前渣油加氢路线包括固定床渣油加氢、沸腾床渣油加氢和浆态床渣油加氢。对于更劣质的渣油,浆态床渣油加氢工艺方案的效益是优于其他方案的。浙江石油化工有限公司采用意大利Eni公司的EST浆态床渣油加氢裂化工艺技术。通过从加工负荷、原料油性质、关键运行操作参数、主要产品收率和性质等方面对2套300×10⁴t/a浆态床渣油加氢装置进行了对比分析,2套装置总体运行情况良好,在现有条件下能够满足80%的加工负荷并平稳运行,转化率达到90%以上,液体收率达到75%左右,石脑油、柴油和蜡油等产品质量能够满足下游二次加工装置的要求。同时也重点剖析了在装置运行过程中遇到的减压塔无法长周期运行、螺旋板换热器内漏、浆液系统结焦堵塞、催化剂单耗高、仪表测量偏差大等生产难题,并提出了相应的解决措施和方案。     

南蒸馏—减粘装置节能优化组台改造

锦西石化分公司南蒸馏—减粘装置优化组合改造是一项重大的节能措施，该项目对减粘装置进行搬迁改造，与南蒸馏装置形成联合装置。通过合理规划减底渣油物料流向，减少中间过程能量损失，同时降低了两套装置的能耗。     

俄罗斯原油评价数据及加工流程的优化选择

原油评价是在实验室对原油进行一系列分析和馏分切割,分析原油和各段馏分油的性质,确定产品分布及产品收率,为制定原油加工流程提供优化方案,以生产出合适的产品,使原油资源得到合理利用。原油评价认为,俄罗斯原油属于含硫中间基原油,初馏点至180℃石脑油馏分经石脑油加氢精制后,分离出液态烃、轻石脑油及重石脑油;150~230℃喷气燃料馏分进入加氢精制装置,生产3号喷气燃料或柴油调和组分;200~350℃柴油馏分进入柴油加氢精制装置,生产合格的柴油产品;350~560℃混合蜡油馏分进入加氢裂化装置,生产石脑油、高品质航空煤油(3号喷气燃料)及柴油;大于560℃渣油馏分经渣油加氢精制后,可作为催化原料直接进入重油催化裂化装置。俄罗斯原油的盐含量为24.0mg/kg,在加工过程中,容易形成"HCl-H2S-H2O"腐蚀,对设备影响较大,要重视工艺防腐和设备防腐。     

改善渣油加氢脱硫和重油催化裂化组合工艺加工灵活性的研究

渣油加氢脱硫和重油催化裂化装置的组合工艺轻油收率高、生产过程清洁,在国内新建或改扩建炼油项目中广泛应用。但由于固定床渣油加氢脱硫技术本身的限制,其加工原料的重金属、沥青质和残炭等不得不限定在一定范围内,因此加工原油的灵活性有所限制。以新建设计加工沙特中质原油12.5Mt/a炼油厂为例,核心重油加工装置采用4.0Mt/a渣油加氢脱硫和3.50Mt/a重油催化裂化装置组合工艺,在此基础上增加1.20Mt/a延迟焦化装置,改善项目的加工灵活性和原油适应性,渣油加氢装置的进料优化为92.5%负荷,进料中的杂质含量降低约10%。在渣油加氢脱硫装置定期换剂过程中,不需更换原油,全厂的加工负荷可以维持在80%以上,保证了各工艺装置在合理负荷下运行。且将0.24Mt/a催化油浆进行热裂化转化,解决了催化油浆的出路问题,增加了经济效益,同时可以把重污油和含油污泥进行清洁化无害处理,实现了项目的重油加工灵活性和清洁化生产。     

渣油加氢技术进展

在重质原油加工利用上,加氢路线较脱碳路线的重油转化深度高、资源利用率高、经济效益好,但反应条件苛刻,流程复杂,能耗与投资比脱碳路线高。随着原油劣质化及日益严格的环保要求,渣油加工选择加氢路线会越来越多。固定床加氢工艺是通过不同床层的不同类型催化剂,对重油中的金属杂原子和硫、氮元素进行脱除以及对重组分进行改质,技术最为成熟。目前移动床加氢技术主要用作固定床工艺的前置反应器系统,是移动床与固定床的组合工艺。沸腾床加氢裂化原料油适应性广,反应器内温度均匀,催化剂可在线加入和排除,运行周期长,传质传热好,渣油转化率高,装置操作灵活。渣油悬浮床加氢裂化在建装置不多,然而其渣油原料转化率和轻油收率都比延迟焦化和沸腾床加氢裂化高得多,工业应用前景乐观。当渣油原料Ni+V小于120μg/g时,固定床渣油加氢是首选;为延长装置运转周期,可在固定床反应器前增加移动床反应器;加工高残炭、高金属含量减压渣油,沸腾床渣油加氢裂化技术是首选;悬浮床渣油加氢裂化为未来加工更重、更高金属含量及残炭的渣油做好了技术准备。     

兴古潜山油藏高温阻垢剂研制

辽河油田兴古潜山油藏生产井结垢现象日益严重,其中电潜泵井结垢率为100%,抽油机井结垢率达60%,降低了油井产量,造成生产管线或设备堵塞。统计发现,井筒中结垢主要发生在射孔井段以上、动液面以下(温度45℃以上)的套管、尾管、油管、抽油泵、抽油杆上,具体表现为筛管、尾管堵塞,垢卡抽油泵,双凡尔漏失,抽油杆断脱,油管磨穿等现象,现有的防垢剂在潜山160℃的油层条件下无法满足生产需要。为此,开展了兴古潜山油藏高温防垢技术研究。通过潜山地层水质分析,总结了该块结垢原因及规律,研制出高分子团结构的高温阻垢剂,经过室内试验,验证其在160℃的高温下仍具有85%的防垢率。通过50余井次现场试验表明,从井口加入耐高温防垢剂后,井筒及地面管线的结垢现象明显减少,管线压力平稳,未影响油井产量,保证了兴古潜山油藏生产顺利进行。     

Characterization of Crude Oils and Their Fouling Deposits Using a Batch Stirred Cell System

A small (1 L) batch stirred cell system has been developed to study crude oil fouling at surface temperatures up to 400°C and pressures up to 30 bar. Fouling resistance–time data are obtained from experiments in which the principal operating variables are surface shear stress, surface temperature, heat flux, and crude oil type. The oils and deposits are characterized and correlated with the experimental heat transfer fouling data to understand better the effects of process conditions such as surface temperature and surface shear stress on the fouling process. Deposits are subjected to a range of qualitative and quantitative analyses in order to gain a better insight into the crude oil fouling phenomenon. Thermal data that can be obtained relatively quickly from the batch cell provide fouling rates, Arrhenius plots, and apparent activation energies as a function of process variables. The experimental system, supported by computational fluid dynamics (CFD) studies, allows fouling threshold conditions of surface temperature and shear stress to be identified relatively quickly in the laboratory. The data also contribute to existing knowledge about the compensation plot.     

Correlating Field and Laboratory Data for Crude Oil Fouling

Crude oil fouling in a laboratory fouling unit was investigated. The study focused on the preheat-train heat exchangers located just before the crude unit furnace and operating at temperatures in excess of 200C. A fouling rate model developed using laboratory data from crude blends was used to predict the threshold conditions where negligible fouling was expected under refinery conditions. The results from the model were compared to actual data from a fouling unit located at a refinery. The article discusses factors that may explain the performance of the model and the observed discrepancies between fouling data obtained in the laboratory and the field.     

Fouling Management of Thermal Cracking Units

ABSTRACT

Visbreakers and other thermal cracking units are thermal process units in crude oil refineries that upgrade heavy petroleum, usually residual oils produced from atmospheric or vacuum distillation of crude oil. The associated process streams of these units consist of heavy hydrocarbons with very high viscosities and impurities, resulting in fouling of the heat exchangers used to cool or heat these streams. This paper presents a practical fouling analysis for thermal cracking units in a refinery in Germany. Fouling management at this refinery was initiated as part of the refinery energy-saving program. Following similar analysis of the refinery's crude preheat trains, heat exchanger networks associated in the thermal cracking units were modeled by entering the plant monitoring data, network topology, and heat exchanger geometries into a commercial heat exchanger network simulator, SmartPM. Fouling behaviors of vacuum residue streams and thermal cracker residue streams were identified and quantified. Both chemical reaction fouling and particulate fouling mechanisms were identified to be responsible for the fouling in these streams. Dynamic fouling models were fitted and used to predict fouling of these heavy petroleum streams, which fouled on both the shell and tube sides of the shell-and-tube heat exchangers.     

Effects of Mitigating Fouling on the Energy Efficiency of Crude-Oil Distillation

An analysis was performed to determine the effects of fouling of the preheat train on the energy efficiency of a typical crude-distillation unit with a capacity of 100,000 bbl/day. A spreadsheet analysis was developed to calculate the thermal duty for each of the heat exchanger groups that heat the crude oil from ambient conditions to the distillation temperature. A fouling-rate model developed in a previous study was applied to calculate the fouling resistance as a function of time. Improvements in the energy efficiency were analyzed for different mitigation scenarios. The analysis shows economic incentives for new and improved techniques for mitigating fouling of the preheat train.     

Study on oil fouling in a double pipe heat exchanger with mitigation by a surfactant

Fouling of oils on heat exchanger surfaces and pipelines is a common problem in a variety of industrial applications. This is because the oil deposits on the heat transfer surface causes an increase in pressure drop and a decrease in heat exchanger efficiency. In the current work, oil fouling in double pipe heat exchanger was investigated and mitigated using a surface‐active agent for the flow of a dispersion fluid containing different dispersed oil fractions in water. The effect of the dispersed oil fraction (5%vol and 10%vol) and temperature (35°C‐55°C) on the oil fouling rate was studied and discussed under turbulent flow conditions for both hot and cold fluids. Different amounts of alkylbenzene sulfonate as a surfactant were added to reduce the fouling rate under turbulent flow. It was found that the fouling thermal resistance (R_f) increases when the fluid temperature decreases. The higher the dispersed oil fraction, the higher the R_f for all temperatures due to higher oil deposition. Addition of 0.2%vol to 0.5%vol of alkylbenzene sulfonate caused an appreciable reduction in R_f depending on oil fraction and Reynolds number. The mitigation percent was higher for a lower Reynolds number, reaching up to 96%.     

Use of CFD to Determine Effect of Wire Matrix Inserts on Crude Oil Fouling Conditions

Crude oil fouling rates are strongly affected by both local surface temperature and local surface shear stress. The use of in-tube inserts (such as hiTRAN) in heat exchangers has been shown to be effective in mitigating crude oil fouling while at the same time enhancing heat transfer. However, the introduction of inserts means that there will be axial and radial distributions of both local shear stress and local heat transfer coefficient between the repeating insert–wall contact points, which could mean that there will be local variations in fouling rate. While estimation of local shear stresses and film heat transfer coefficients is facile for bare round tubes, this is no longer the case for tubes fitted with inserts. Accordingly, this article describes a possible solution to the design challenge using computational fluid dynamics (CFD) simulation, the output of which is the temperature and velocity distributions in a three-dimensional geometry of the fluid flow in a tube fitted, for example, with a hiTRAN insert. A simple algorithm is then described for calculating the overall heat transfer coefficient based on the resulting temperature distribution along the wall of the tube. Simulated values of the overall heat transfer coefficient are then compared with those obtained by experiment, showing that there is good agreement, thereby indicating that predicted local values are accurate. Use of CFD in fouling applications now allows the prediction of local conditions when inserts are used and hence can be used to predict whether, and where, fouling might occur.     

Mitigation of Crude Oil Preheat Train Fouling by Design

Fouling in crude oil preheat trains is a significant industrial problem which has restricted the application of process integration techniques such as "pinch technology" in this sector. A semiempirical fouling model for crude oil fouling developed by Panchal and co-workers allows the effects of fouling to be considered at the design stage for such networks. Application of this model at three levels--(1) design of new networks; (2) retrofitting of existing systems; and (3) identification of robust specifications for individual heat exchanger units--is discussed. The design issues are discussed using case studies illustrated by a graphical construction, the temperature field plot. Rigorous optimization of the final designs is not reported. The specification discussion describes how the crude fouling model can be incorporated into existing heat exchanger design software to identify exchanger configurations which are less likely to experience significant fouling over a range of operating conditions. This article concentrates on shell-and-tube designs, but the concepts will be applicable to other exchanger types once a suitable fouling model becomes available.     

Analysis of the influence of operating conditions on fouling rates in fired heaters

Fouling due to chemical reaction in preheat trains for the processing of crude oil plays a key role in the operation and maintenance costs and on greenhouse emissions to atmosphere in crude processing plants. A preheat train consists of a set of heat transfer units that provide the crude oil stream the required amount of thermal energy to reach its target temperature either by heat recovery or by direct firing. Fired heaters supply external high temperature heating through the burning of fuel which result in complex heat transfer processes due to the large temperature and pressure changes and vaporization that takes place inside the unit. In this work, a thermo-hydraulic analysis of the performance of fired heaters is carried out through the application of commercial software to solve the mathematical models using finite difference methods; the analysis is applied to the crude side of a vertical fired heater in order to evaluate the impact of process conditions such as throughput and crude inlet temperature (CIT) on the fouling that take place at the early stages of operation. Using a fouling rate model based on thermo-hydraulic parameters, fouling rates are predicted assuming steady state operation and clean conditions. Although variations in process conditions are known to influence fouling rates, little work has been done on the subject. In this work excess air and steam injection are studied as a means to mitigate fouling. Results show that throughput reduction brings about a marked increase in the fouling rates. A decrease in CIT affects only the convection zone and it is found that this effect is negligible. In terms of excess air, it is found that although it affects negatively the heater efficiency it can be used to balance heat transfer between the convection and radiation zone in a way that fouling rates are reduced; however this strategy should be considered right from the design stage. Finally it is observed that steam injection is an effective method to reduce fouling rates since it results in lower film temperatures and larger shear stress.     

Evaluation of Crude Oil Heat Exchanger Network Fouling Behavior Under Aging Conditions for Scheduled Cleaning

Heat exchanger network (HEN) fouling is an endemic operational challenge prevalent in many process industries. Its impact on both plant operating cost and productivity is significant and can be compounded by aging effects of the foulant. In this paper, we model and simulate the effect of aging on tube-side fouling and cleaning dynamics in a crude oil refinery preheat train (PHT) comprising a 14-unit HEN. A prescient, HEN modeling and dynamic simulation were performed wherein the transients of fouling and aging as well as the interactions between individual units were captured. To assess the temporal effects, different crude oil deposit (gel) aging scenarios (no aging vs. slow, medial, and fast aging) in the downstream units were considered for the PHTs’ overall heat recovery, cleaning options, and operability. The results show that the deleterious impact of fouling and concomitant aging, quantified in terms of thermal resistances, was significantly reduced by fast aging as opposed to medial, slow, or no aging of the gel deposit. Faster aging rate reflected improved heat recovery and a lesser demand for and lower cost of PHT cleaning. The concomitant higher growth of coke deposit due to aging, however, resulted in greater hydraulic resistance, which is inimical to operability.     

Fouling of Some Canadian Crude Oils

A thermal fouling study was undertaken using three sour Canadian crude oils. Experiments were carried out in a re-circulation fouling loop equipped with an annular (HTRI) electrically heated probe. Fluids at pressures of about 1000–1340 kPa under a nitrogen atmosphere were re-circulated at a velocity of 0.75 m/s for periods of 48 hours, and the decline in heat transfer coefficient followed under conditions of constant heat flux. Bulk temperatures were varied over a range of 200–285^?C, and initial surface temperatures ranged from 300–380^?C. Heat fluxes were in a range of 265–485 kW/m².

Surface temperature effects on fouling of the three oils were compared, and fouling activation energies were estimated. For the lightest oil, a more detailed study of velocity and bulk and surface temperature effects was carried out. The fouling rate decreased slightly with increasing velocity but increased with both surface and bulk temperatures; a rough correlation was developed using a modified film temperature weighted more heavily on the surface temperature. Deposits showed high concentrations of sulfur and minerals, indicating the importance of iron sulfide deposition.