Shutdown Strategy for Flare Minimization at an Olefin Plant

Shutdown operations in olefin plants generate extensive flare emissions, which cause adverse environmental and societal impacts as well as large amounts of raw material and energy losses that could supposedly be unitized to generate much more needed products. Consequently, shutdown optimization for flare minimization is crucially important to all stake holders. However, the current practice for shutdown flare minimization almost exclusively depends on experienced operators, engineers, and plant administration. There is still a lack of systematic studies on how to cost‐effectively identify and examine shutdown flare minimization strategies through plant‐wide modeling and simulations. A novel process retrofit and shutdown operation strategy for flare minimization in an olefin plant is introduced. Plant‐wide dynamic simulations are employed to examine the operational feasibility and critical information during the plant shutdown operation. The proposed shutdown strategy could virtually reduce the flare emission significantly compared to historical records.     

Safety‐Considered Proactive Flare Minimization Strategy under Ethylene Plant Upsets

Ethylene plant upsets usually lead to flaring of off‐spec products, resulting in significant losses of raw material and energy as well as to air emission problems. Under the premise of plant safe operation, establishing process recycles connecting off‐spec streams to their upper‐stream process can help to reduce flaring during plant upsets. Operational strategies for recycling the potential flaring sources, i.e., effluents from the acetylene reactor and ethylene tower overhead, under various process upsets are developed and analyzed based on rigorous plant‐wide dynamic simulations. Safety considerations on the compressor system performance have been addressed by quantitative comparison of the effectiveness of various recycling strategies. Case studies demonstrate that the safety‐considered flare minimization strategies can proactively reduce the flaring emission amount and upset time and thus have great potentials of economical and environmental benefits to ethylene plants.     

控制系统在超级克劳斯反应中的应用

新能凤凰公司硫回收装置是引进的荷兰公司的三级克劳斯及超级克劳斯成套设备,工艺先进、成熟、系统平稳,装置控制特点突出。在开停车过程及日常控制中采用了Foxboro公司的DCS控制系统,联锁紧急停车采用的是Tricon公司的SIS系统进行控制,及控制中所存在的问题解决,进而充分回收硫生成硫磺实现达产目标,同时要达到环保排放标准进行排放,从而减少对环境的污染。     

乙烯装置开停车过程节能减排技术进展

随着我国乙烯装置的大型化、原料价格的增长以及环保要求的日益严格,乙烯装置开停车过程的节能减排研究逐渐受到乙烯企业和国内外研究者的重视。综述了国内外关于乙烯装置开停车过程中的节能减排技术,并对动态模拟在开停车节能减排中的应用进展进行了介绍。     

Combustion mechanism development and CFD simulation for the prediction of soot emission during flaring

Industrial Flares are important safety devices to burn off the unwanted gas during process startup, shutdown, or upset. However, flaring, especially the associated smoke, is a symbol of emissions from refineries, oil gas fields, and chemical processing plants. How to simultaneously achieve high combustion efficiency (CE) and low soot emission is an important issue. Soot emissions are influenced by many factors. Flare operators tend to over-steam or over-air to suppress smoke, which results in low CE. How to achieve optimal flare performance remains a question to the industry and the regulatory agencies. In this paper, regulations in the US regarding flaring were reviewed. In order to determine the optimal operating window for the flare, different combustion mechanisms related to soot emissions were summarized. A new combustion mechanism (Vsoot) for predicting soot emissions was developed and validated against experimental data. Computational fluid dynamic (CFD) models combined with Vsoot combustion mechanism were developed to simulate the flaring events. It was observed that simulation results agree well with experimental data.

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石化企业挥发性有机物无组织排放监测技术进展

无组织排放占石化企业挥发性有机物（VOCs）排放的主导地位,排放点多、面广、量大、分散、无规则,总体表现为大型面源或体积源,监测难度很大。本文评述了点、线和面(通量)等VOCs无组织排放监测技术及应用进展,总结了石化企业VOCs无组织排放监测存在的主要问题与难点,提出了石化企业VOCs无组织排放监测体系及适用监测技术。总体上,石化企业VOCs无组织排放监控存在排放清单质量不高、源头监测及溯源困难、排放烟羽及其迁移扩散途径无定形、厂界等开放空间难以封闭监测、常规监测的时间和空间覆盖有限等问题或技术难点,可复合应用点、线、面及通量监测技术,结合常规离线、实时在线、排放通量、移动快速响应等监测设计,构建覆盖排放与环境影响的多元化、网络化、立体化监控体系。未来石化企业VOCs无组织排放监控将向多层级、智能化和大数据应用发展。     

Multi-objective optimization methodology to size cogeneration systems for managing flares from uncertain sources during abnormal process operations

Flaring is common practice in industries to reduce the risk during abnormal situations, to maintain the product quality or to operate safely during process start up and shut down. Due to its large negative impacts on the environment and society, various protocol and steps, i.e., Kyoto protocol, the United Nations Environment Programme, have been created for future mitigation. There is significant amount of heating value lost during flaring events. A cogeneration (COGEN) system can use waste flare streams as fuel to generate heat and power within a process. The objective of this work is to develop an optimization framework for sizing a COGEN unit to manage flares from uncertain sources by minimizing the overall cost and emissions of greenhouse gases. Multi-objective trade-offs between the economic, environmental, and energetic aspects are presented through Pareto fronts for a base case ethylene plant using a stochastic optimization technique based on genetic algorithm.     

Optimal operation of process plants under partial shutdown conditions

A systematic strategy for optimal plant operation during partial shutdowns is proposed. We consider the situation where one or more process units are shut down due to failure or maintenance but where the remaining units are able to continue operation to some degree. The goal of the strategy is to manipulate the plant degrees‐of‐freedom—during and after the shutdown—such that production is restored in a cost‐optimal fashion while meeting safety and operational constraints. Optimal control trajectories are obtained through the solution of a dynamic optimization problem. A novel multitiered optimization approach allows the prioritization of multiple competing objectives and the specification of trade‐offs between them. Uncertainty in the downtime estimate, a crucial parameter in shutdown optimization, is addressed through reoptimization. We employ a transient predictive control algorithm for implementing the computed control policy under feedback. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4151–4168, 2013     

石化装置改扩建对火炬系统负荷影响的量化分析

火炬是大型石油化工联合装置必备的辅助生产设施,同时也是重要的安全环保措施。但目前火炬的设计标准《石油化工可燃性气体排放系统设计规范》（SH 3009—2013）或者国际标准《泄压和减压系统》（API 521）主要还是基于行业惯例和工程经验。新增装置或扩建装置会对火炬系统造成较大的风险影响,尤其是在火炬系统管网管径及管网布置不改变或无法改变的情况下。本文提出了一种针对石化联合装置进行改扩建对火炬系统风险评估的通用方法,采用改扩建前后发生多泄放源同时泄放的叠加方法流程来获得火炬系统关键参数。采用Aspen Flare-net软件进行数值模拟和案例研究,获得了厂区新增装置导致的火炬系统安全阀背压、噪声等数值结果及对应的安全隐患,并得到了全部可能导致火炬系统安全隐患的泄放组合,为泄放负荷管理提供了量化决策依据,同时说明了所提方法的应用效果和有效性。     

A method to refine the start-up scheme of compression and refrigeration systems in ethylene plants via dynamic simulation

Starting the cracking gas compressor and precooling the refrigeration system are keys to start-up of an ethylene plant and accounts for up to 50% of the total start-up time and plant flare emissions. Premature feeding of cracking furnaces can be avoided if the cracking gas compressor is started and the refrigeration system is precooled in advance using mixed gas as the start-up working medium (SWM). Start-up scenario with mixed gas as SWM could significantly reduce the emission loss and shorten the precooling time. Research shows that making appropriate start-up scheme is important not only to ensure operational safety and feasibility, but also to reduce energy consumption. In this paper, a method is proposed to select suitable start-up operational parameters of compression and refrigeration system with sufficient safe operating ranges and short precooling time. The complex interrelation among key parameters of start-up is analyzed. It is found that higher energy consumption, especially for super high-pressure steam (SS), can promote operational safety and shorten the precooling time during start-up. Based on steady-state and dynamic simulation, appropriate operating parameter ranges are determined with reasonable SS consumption. A real case study demonstrates that an appropriate start-up scheme will optimize the operation.     

Atmospheric protection at coke plants

Atmospheric protection at coke plants is assessed on the basis of plant records and experimental data. Problems in addressing atmospheric emissions are often associated with poor inventories of emission sources. On the basis of research at OAO VUKhIN, a standard regarding the determination of atmospheric emissions is developed. This standard ensures objectivity of the data. Russian and European standards regarding atmospheric emissions are compared. It is clear that the planned introduction of a new system of technical standards for emissions requires the review of all atmospheric-protection measures and the introduction of new approaches.     

A GIS-based national emission inventory of major VOCs and risk assessment modeling: Part I — methodology and spatial pattern of emissions

This paper presents a method for assessing and managing the South Korean atmospheric emission inventory of volatile organic compounds (VOCs) based on a geographic information system (GIS). The use of this GIS-based assessment technique makes it possible to obtain the geographical characteristics of anthropogenic emission sources, observe spatial patterns within the emission inventory, and develop a new bottom-up method for improving the spatial accuracy of emission inventories. As a case study, we estimated the emission rates of five major VOCs (benzene, ethylbenzene, styrene, toluene, and xylene) throughout South Korea for the year 2004. The spatial pattern of emissions and relative contributions of various sources showed considerable spatial variability. A comparison of estimated emissions data and observed environmental concentration revealed a reasonable degree of accuracy for the estimated values. The proposed methodologies and information provided in this study can assist in the development of environmental policy, and can be adopted internationally to obtain a more precise emission inventory.     

Assessing the environmental risk of coke production

The environmental risk due to atmospheric pollution from coke plants is considered, with respect to all organized and unorganized sources of emissions in the coal-preparation, coal-enrichment, coke-production, byproduct-trapping, benzene-rectification, and tar-processing shops. The chronic noncarcinogenic risk is within the acceptable limits for 30% of all the organized emission sources, high for 23.3% of the sources, and very high for 47.7% of the sources; the carcinogenic risk exceeds acceptable levels for 49.6% of sources.     

Optimal response under partial plant shutdown with discontinuous dynamic models

This work describes mathematical formulations for modeling aspects of partial shutdowns in multiunit plants. The specific type of partial shutdown considered is one that permits the decoupling of affected units from the rest of the plant, thus enabling continued plant operation, albeit in a more limited fashion. Parsimonious and computationally efficient mixed-integer formulations are presented for specific discontinuous phenomena that arise in partial shutdown modeling, such as shutdown thresholds, induced shutdowns, discontinuous costs, and minimum shutdown durations. It is demonstrated that induced shutdowns (secondary shutdowns triggered by the original shutdown) can be correctly penalized in the objective by capturing the shutdown's true discontinuous economic cost. The computed optimal solution is implemented in closed-loop by employing a multitiered model predictive shutdown controller, in which a discrete-time mixed-integer dynamic optimization (MIDO) problem is embedded. Both objectives of maximizing economics and minimizing restoration (shutdown recovery) time are considered.     

尿素大修停车时如何防止环境污染

探讨大型尿素装置在大修停车时间防止环境污染,并对装置停车时优化操作和防治污染提出了一些新观点。     

Bioprocesses for the removal of nitrogen oxides from polluted air

Nitrogen oxides (NOx) of environmental concern are nitrogen monoxide (NO) and nitrogen dioxide (NO₂). They are hazardous air pollutants that lead to the formation of acid rain and tropospheric ozone. Both pollutants are usually present simultaneously and are, therefore, called NOx. Another compound is N₂O which is found in the stratosphere where it plays a role in the greenhouse effect. Concern for environmental and health issues coupled with stringent NOx emission standards generates a need for the development of efficient low‐cost NOx abatement technologies. Under such circumstances, it becomes mandatory for each NOx‐emitting industry or facility to opt for proper NOx control measures. Several techniques are available to control NOx emissions: selective catalytic reduction (SCR), selective non‐catalytic reduction (SNCR), adsorption, scrubbing, and biological methods. Each process offers specific advantages and limitations. Since bioprocesses present many advantages over conventional technologies for flue gas cleaning, a lot of interest has recently been shown for these processes. This article reviews the major characteristics of conventional non‐biological technologies and recent advances in the biological removal of NOx from flue gases based on the catalytic activity of either eucaryotes or procaryotes, ie nitrification, denitrification, the use of microalgae, and a combined physicochemical and biological process (BioDeNOx). Relatively uncomplicated design and simple operation and maintenance requirements make biological removal a good option for the control of NOx emissions in stationary sources. Copyright © 2005 Society of Chemical Industry     

合成橡胶装置挥发性有机物排放治理措施

介绍中国石油独山子石化公司乙烯厂丁苯橡胶装置挥发性有机物(VOCs)排放治理措施。通过有针对性地对装置压力控制模式、处理工艺、停工检修过程、排放口治理、后处理设备、溶剂系统运行条件、密封面等方面实施环保控制及优化措施,现场VOCs排放减少,环境明显改善。     

Biological treatment of a contaminated gaseous emission from a paint and varnish plant—from laboratory studies to pilot‐scale operation

A Vapour‐Phase Bioreactor (VPB), namely a biotrickling filter, was scaled‐up and operated in‐situ for the treatment of gaseous emissions from a paint and varnish industrial plant. A microbial culture able to degrade the target compounds was enriched and a laboratory‐scale VPB was established in order to evaluate the treatment's performance. The VPB presented removal efficiencies higher than 90% when exposed to Organic Loads (OL) of ca 50 g h^?1 m^?3 of reactor. The VPB was exposed to dynamic conditions often found in‐situ (eg night and weekend shutdown periods) and showed a fast capacity to recover, with and without mineral medium recirculation. After a prolonged interruption period (10 months), the VPB was not able to cope with OL of ca 25 g h^?1 m^?3 of reactor and re‐inoculation was required in order to recover the treatment performance. The VPB also showed limited treatment when exposed to higher OL (ca 500 g h^?1 m^?3 of reactor). The VPB was then scaled‐up and a 3 m³ VPB was operated in‐situ, showing removal efficiencies higher than 50% when exposed to an OL of c 5 g h^?1 m^?3 of reactor, thus complying with current legal demands. The addition of a maintenance feed was shown to be a useful tool for VPB pilot‐scale operation when shutdown periods occurred. A factorial design of experiments was carried out, which allowed reduction to one‐tenth of the initial supply of the main mineral medium constituents, namely phosphate buffer, ammonium and magnesium salts, and also elimination of the metal supplement. Overall, the VPBs were shown to be robust equipment, being able to respond actively to dynamic treatment scenarios, particularly night and weekend shutdown periods. Copyright © 2003 Society of Chemical Industry     

裂解装置开车过程减少火炬排放的探讨与实践

随着裂解装置的大型化,其开车的成本也不断增大,同时火炬排放对环境的影响也越来越大,如何降低开车成本和火炬排放对环境的影响,成为企业关注的问题。通过对镇海炼化1000kt／a裂解装置两次开车过程的对比,探讨裂解装置减少火炬排放降低开车成本的措施。     

Liquid Fuels from Alternative Carbon Sources Minimizing Carbon Dioxide Emissions

The energy needs of the world continue to grow, as does the resulting environmental impact. Policy makers continue to call for alternative energies to replace today's petroleum‐based liquid fuels. However, liquid fuels have significant advantages, and it is probably unwise to abandon the existing infrastructure without appropriately exploring alternatives to lessen the environmental burden of producing liquid fuels. Biomass and coal are often proposed as alternatives to petroleum‐based carbon sources, but those processes lose a significant amount of their potential product to unwanted carbon dioxide emissions. However, combining biomass and coal with cleaner natural gas yields processes with less environmental impact to produce liquid fuels with small, zero, or even negative carbon dioxide emissions. Our process synthesis approach is applied to commonly encountered liquid fuel production methods to identify promising routes and to establish feasibility limits on those less promising alternatives. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2062–2078, 2013