Sour Water Stripping Research Articles

Application of membrane contactors to remove hydrogen sulfide from sour water

Wastewater containing hydrogen sulfide (H2S), also known as sour water, is a byproduct stream generated during oil & gas (O&G) production. Because H2S is both toxic and corrosive, treatment to remove it is generally practiced, either by chemical treatment or stripping. Within the O&G industry, sour water strippers are generally used, especially when there is a need for recycle/reuse or for safe handling. However, those treatment processes have limitations in terms of chemical consumption or high capital cost (due to expensive materials of construction). Commercially available membrane contactors are a potential alternative technology for sour water treatment with advantages such as low capital cost, modular & compact design and thus, portability. The hydrophobic character of the membrane allows H2S gas from the sour water to permeate through, while preventing the passage of water. When applied in this novel approach, the H2S passing through the membrane dissolves into a receiving solution containing a chemical, e.g. amines or sodium hydroxide, which immediately converts the H2S to a non-hazardous form thereby maximizing the concentration gradient across the membrane. Process performance has been evaluated by coupling experimental data with mass transfer equations, using the overall mass transfer coefficient as the process performance indicator. Experiments showed a mass transfer coefficient of 0.243cm/min for both gas field sour process water and synthetic solutions, indicating no immediate membrane fouling. This process could be implemented in gas processing facilities or refineries with an amine regeneration unit as a side stream of the amine could be used as the receiving solution. It also has potential as a “fit-for-purpose” solution for groundwater treatment and other niche applications.

Heat integration of phenols and ammonia recovery process for the treatment of coal gasification wastewater

Coal gasification wastewater with high concentration of phenols and ammonia is difficult to biodegrade. Phenols and ammonia recovery process consisting of the sour water stripper, extraction and the solvent recovery system is applied to removing these pollutants. An improved phenol and ammonia recovery process that the sour water stripper and the solvent recovery system are thermal integrated is proposed based on the conventional wastewater treatment process. Therein, the ammonia-rich gas drawn from the middle of sour water stripper, as a heat source, is exchanged with the reboiler of the solvent distillation column and the solvent stripper. The results show that the operating cost is about 34% less than that of the conventional process, and the TAC can be decreased by about 30.8%. The proposed process of phenols and ammonia recovery for the coal gasification wastewater is proven to be an effective and economical process with a good application prospect.

Development of a novel processing system for efficient sour water stripping

Application of vapor recompression systems can result in enhanced energy efficiency and reduced energy requirements of distillation systems. In vapor recompression systems, temperature and dew point temperature of the top product of the column are increased through compression. By transferring heat from top to bottoms product, required boil up and reflux streams for the column are provided. In this paper, a new system is proposed for efficient stripping of sour water based on vapor recompression. Ammonia and H2S are the contaminants of sour water. Initially, based on a certain specifications of products, a sour water stripping system is implemented. A novel processing system is then developed and simulated to reduce utility requirements. The two processing systems are economically evaluated by Aspen Economic Evaluation software. There are 89.0% and 83.7% reduction of hot and cold utility requirements for the proposed system in comparison to the base processing system. However, the new processing system requires new equipment such as compressor and corresponding mechanical work that increases its capital and operating costs in comparison to the base case. However, the results indicate that the proposed system results in reduction of 11.4% of total annual costs and 14.9% of operating costs.

Process Simulation for Removing Impurities From Wastewater Using Sour Water 2-Strippers system via Aspen Hysys

Abstract In this paper, Aspen Hysys v8.8 was used to simulate two strippers for sour water stripping process as the aim for removal of chemical impurities such as hydrogen sulfide, carbon dioxide and ammonia in wastewater. As a result of elimination of these impurities, the water can be reused. Comparison between single and two strippers and elevating the stripping efficiency was the objectives of the present study. The feed flow rate and compositions were specified according to the typical Chevron WWT process conditions. The simulation result shows that 100 % ammonia was stripped into the two stripper system but only 24 % stripped in the single stripper system. The result of H2O was almost same in both systems. The stripped water collected via the bottom of the Ammonia Stripper contains less than 10 ppm of hydrogen sulphide and less than 50 ppm of ammonia.

Large scale optimization of a sour water stripping plant using surrogate models

In this work, we propose a new methodology for the large scale optimization and process integration of complex chemical processes that have been simulated using modular chemical process simulators. Units with significant numerical noise or large CPU times are substituted by surrogate models based on Kriging interpolation. Using a degree of freedom analysis, some of those units can be aggregated into a single unit to reduce the complexity of the resulting model. As a result, we solve a hybrid simulation-optimization model formed by units in the original flowsheet, Kriging models, and explicit equations. We present a case study of the optimization of a sour water stripping plant in which we simultaneously consider economics, heat integration and environmental impact using the ReCiPe indicator, which incorporates the recent advances made in Life Cycle Assessment (LCA). The optimization strategy guarantees the convergence to a local optimum inside the tolerance of the numerical noise.

Erosion corrosion failure analysis of the elbow in sour water stripper overhead condensing reflux system

The erosion corrosion failure of elbow of one oil refinery was investigated by using Aspen software, CFD technology and experiments. And the gas–liquid equilibrium distribution of H2S and NH3 and multiphase flow simulation in the overhead system of a sour water stripper were obtained. The result shows that the component mole fraction of H2S and NH3 rises markedly with decreasing temperature. At the outlet of air cooler, the temperature drops to 85°C to form high concentration of ammonium bisulfide (NH4HS), which would cause serious erosion corrosion at a certain flow rate and reveals an inhomogeneous thinning. The liquid phase fraction mainly distributes on the outside part of elbow, the more sour water accumulates there resulting in localized corrosion thinning. Meanwhile, the experiments show that when the concentration of NH4HS reaches 10wt.%, the corrosion rates increase rapidly with increased velocity. Thus controlling the concentration of NH4HS below 10wt.% in reflux drum would reduce the risk of erosion corrosion failure.

Improving energy efficiency of distillation using heat pump assisted columns

ABSTRACTDistillation is a widely used separation technique in process industries, although it requires substantial energy inputs. In this study on improving the energy efficiency, both compression and absorption type heat pumps along with feed preheat are analyzed for two common distillation processes of a typical petroleum refinery, to recover waste heat at lower temperatures by upgrading it to useful temperature levels. The heat pumps are also coupled with intermediate heat exchangers (HEXs) to improve cost savings further. The case studies in this investigation are sour water stripper and the C4 separation unit consisting of a deisobutanizer and debutanizer; these include distillation with a partial condenser and separation of compounds having wide boiling points, which have not been studied earlier. Results from these case studies indicate that heat pumps can generally achieve attractive cost savings and that further addition of intermediate HEXs usually worsens the payback, mainly due to additional capital cost. However, intermediate HEXs are beneficial for cases where heat pump application between condenser and reboiler is not economical or feasible, especially in the case of distillation operations requiring very high temperature lifts. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.

Direct production of gasoline and diesel fuels from biomass via integrated hydropyrolysis and hydroconversion process—A techno‐economic analysis

A techno‐economic analysis (TEA) is performed to investigate the production of gasoline and diesel range hydrocarbon fuels by conversion of woody biomass via Gas Technology Institute (GTI)'s integrated hydropyrolysis plus hydroconversion (IH2) process. The processing capacity is 2000 dry metric tonnes (2205 dry US tons) of woody biomass per day. Major process areas include catalytic hydropyrolysis, catalytic hydroconversion, on‐site hydrogen production, feedstock handling and storage, hydrocarbon absorber, sour water stripper, hydrogen sulfide scrubber, distillation tower, and all other operations support utilities. The TEA incorporates applicable commercial technologies, process modeling using Aspen HYSYS software, equipment cost estimation, and discounted cash flow analysis. The resulting minimum fuel selling price is $1.64 per gallon (or $1.68 per gallon of gasoline equivalent) in 2007 US dollars. The process yields 79 gallons of liquid fuels per dry US ton of woody biomass feedstock, for an annual fuel production rate of 61 million gallons at 96% on‐stream time. The estimated total capital investment for an nth‐plant is $264 million. A sensitivity analysis captures uncertainties in costs and plant performance. Results from this TEA can serve as the baseline for future comparison and as a basis for comparing this process to other biomass‐to‐liquid fuel pathways. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 609–617, 2014

An automated environmental and economic evaluation methodology for the optimization of a sour water stripping plant

Abstract In this work a real sour stripping plant of a petrochemical complex simulated in AspenHysys® is improved using an automated tool programmed in Matlab®. The new developed procedure provides the performance evaluation and the comparison between different alternatives of the plant through the calculation and aggregation of environmental and economic indicators. The results obtained give insights into the plant environmental behavior, being very useful to find the suitable modifications in operation and topology of the plant. Moreover, the use of this tool allows the implementation of optimization algorithms and heat integration strategies, with the aim of minimizing resources consumption, pollutants releases, energy requirements and total costs. Specifically, the procedure helps to significantly improve the performance of the studied process: the operating costs are reduced near 8%, while the amount of released CO2-eq is 7% lower, and the process consumes 66% less water.

Significance of Kaduna River to Kaduna Refining and Petrochemicals Complex: Some Checks and Balances

Kaduna Refinery and Petrochemicals Complex comprises of variousprocessing units. The plants produce various grades of petroleum andpetrochemical products. But in all of the plants and facilities, water isrequired in its various forms. The paper describes Desalter Process andRefinery Wastewater. The only major source of water is Kaduna River. TheChemical compositions of the raw and filtered water differ. The compositionsof the treated and “imported” bottled waters are the same and thus fit fordrinking. pH value is fairly constant and so also other elements. Purificationis by demineralization using ion-exchange resins. Demineralised watercontains a number of chemicals and compounds. The process waters aredischarged either as steam or drained out as affluent water. The Sour WaterStripper (SWS) is not functioning. Consequently, the polluted wastewater isdischarged directly to the environment. The Sour Water Stripper must beresuscitated and made to function. Government and KRPC would need toinform and educate members of the community about the effluent wastewaterand its consequences in the environment. Ultra Filtration Membrane Systemis recommended for treatment of desalter effluent.

Enhancing Abnormal Events Management by the Use of Quantitative Process Hazards Analysis Results

Thorough process abnormal events management (AEM) requires accurate fault diagnosis and also a complete supporting system for making correct decisions. In this work, an effective and dynamic integration of AEM and process hazards analysis (PHA) is carried out. In the integrated system, the HAZOP analysis is extended for its use as a supporting tool when facing online abnormal situations. Thus, the extended HAZOP analysis includes quantitative information, in the form of key variables thresholds, and incorporates a set of corrective actions (CAs) to mitigate the harmful considered consequences. The dynamic integration is achieved by generating a protocol where CAs are ranked by the seriousness and urgency of the consequences that they mitigate. The supporting system is developed in a Matlab and Aspen Dynamics integrated framework. An industrial sour water stripping plant is used as case study.

Retrofit of sour water networks in oil refineries: A case study

A case study is presented of the retrofit of a sour water network in a petroleum refinery that generates 581,000 m 3/yr of sour water. Flowrates and contaminant levels of ammonia and hydrogen sulfide were traced for all major water streams in the sour water network. By grouping some process units, a reuse scheme was found that only generates 280,000 m 3/yr of sour water, saving 83% of freshwater and 52% in energy and CO 2 emissions associated with pumping and the heat requirement to scrub out the sour components. Additionally, it was found that the remaining water, after treatment in the sour water stripper, could be reused elsewhere in the plant, if cyanide ions were eliminated. This case study has provided the foundation for further plant studies to validate the water profile of the proposed scheme.

Catalytic destruction of NH 3 and SO 2 over alumina supported transition metal oxides

The catalytic destruction of NH 3 and SO 2 has been examined over a series of alumina supported transition metal oxide catalysts in the laboratory. It was found that alumina supported vanadium oxide is the best candidate for this reaction. These studies show that employing a feed containing 4% NH 3 + 3% SO 2 and a residence time of 0.75 s at 700 °C, conversions of 100 and 87.7% for NH 3 and SO 2, respectively, can be achieved over fresh alumina supported vanadium oxide with the main products being only N 2, water and sulfur. The effect of pretreatment of the catalyst by sulfidation was also examined in this study. Based on these results it was shown that feeding a simulated industrial sour water stripper gas (SWSG) plus oxygen over alumina supported vanadium oxide at 750 °C with a residence time of 4 sec, resulted in an NH 3 conversion of 100%, while no SO 2 was detected in the products.

Improvement in steam stripping of sour water through an industrial-scale simulation

Sour water containing hydrogen sulfide, carbon dioxide, hydrogen cyanide, and ammonia is mainly purified by steam stripping. Increased concern in recent times over effluent water quality and energy saving has caused sour water stripping to attract considerable attention. However, the development of the operation methodology and structure of this process has not been systemic, leading to inefficiencies in the systems commonly used. In this paper, the characteristics of a sour water stripping column are investigated by using an industrial-scale simulation. From these results, we propose several guidelines (high feed temperature, low composition of CO2 in the feed, need of rectifying section, low mass flow rate of the second recycle stream, high reflux ratio, and modified structure using a pump-around side cooler) for improving stripper performance through changes in the operating condition and process structure. The proposed structure and guidelines can be applied not only to reduce steam consumption and lower the ammonia concentration in the effluent water but also to operate the system stably.

Experimental Investigations of Foaming in a Packed Tower for Sour Water Stripping

A foaming problem in an industrial-size deacidifier (packed column) within the ammonia−hydrogen sulfide circulation scrubbing process (AS process) on a specific site is experimentally investigated. The foamability of solutions is successfully assessed in a small test cell, and the Bikermann coefficient is calculated to characterize the foaminess behavior. The investigations revealed that filtration of the real sour water taken from the specific site does not alter foaming characteristics. Impurities, especially phenol and its derivatives, cresols, are found to highly contribute to foaminess behavior. Experiments in a pilot plant revealed higher pressure drop and lower flood point data. Critical spots of foam formation are identified, and design suggestions for column internals are given.

Dynamic Simulation of the Sour Water Stripping Process and Modified Structure for Effective Pressure Control

As a result of stringent government regulations regarding air and water Pollution, the sour water stripping process has emerged as an important process in petroleum refineries and coke-making works industries. The dynamics of the sour water stripping process have not been revealed as sour water is a weak electrolyte and has nonlinear characteristics. Moreover, in a real plant, there are several problems such as plugging, excessive use of steam, and difficulty in controlling the column pressure. This paper tries to solve these problems and examines controllability. Steady state simulation is used to find the optimal operating conditions. However, the results from the steady state simulation cannot be applied to the actual system directly since the concept of controllability is ignored. Dynamic simulation is used to examine the controllability and the capability of disturbance rejection and to cope with abnormal situations which may occur in real plant. In the actual system, when the ammonia composition in feed increases, the column pressure increases rapidly. The conventional process cannot control the column pressure properly and the system becomes unstable. The proposed structure, with an inter-cooler, gives better performance than the conventional one.

The modified structure of sour water stripping to improve the pressure control

Sour water is mainly purified by steam stripping. In these days, steam stripper has been attracted considerably since effluent water quality and energy saving are getting more important. In this research, several guidelines which can improve stripping performance were proposed. Steady state simulation is used to find out the optimal operating condition. And dynamic simulation is performed to investigate the transient response on the disturbance and to solve control problem when NH3 composition in feed increases. The proposed structure which uses an inter-cooler shows better control performance than the existing facilities.

Hazopexpert: An expert system for automating HAZOP analysis

AbstractHazard and operability (HAZOP) analysis is the study of systematically identifying every conceivable deviation from the design intent, and all possible abnormal causes, and adverse hazardous consequences that can occur in a chemical plant. This is a difficult, labor‐ and knowledge‐intensive, and time‐consuming analysis. HAZOP analysis is typically performed by a group of experts poring over the process P&IDs for weeks. An intelligent system for automating this analysis can reduce the time and effort involved, make the analysis more thorough and detailed, and minimize or eliminate possible human errors. Towards that goal, a model‐based framework has been developed in which the knowledge required to perform HAZOP analysis is divided into process‐specific and process‐general components. The process‐specific knowledge consists of the process material properties and the process P&ID. The process‐general knowledge consists of the HAZOP‐Digraph models of the process units which are qualitative causal models developed specifically for hazard identification. These models are developed in a context independent manner so that they can be used in a wide variety of processes. An inference mechanism is developed for appropriate interaction between these components in order to identify process‐specific abnormal causes and adverse consequences. Based on this framework, an expert system called HAZOPExpert has been developed in an object‐oriented architecture using the expert system shell G2. The salient features of the HAZOPExpert system and its performance on an industrial‐scale sour water stripper plant case study are presented.

Experience with an expert system for automated HAZOP analysis

Hazard and Operability (HAZOP) analysis is the most widely used and recognized as the preferred safety analysis approach in the chemical process industry. A model-based framework and an expert system called HAZOPExpert has been developed recently for automating this analysis. The performance of HAZOPExpert was evaluated on a sour water stripper plant and a hydrotreator plant case studies. The expert system was found to successfully emulate the human experts reasoning and identify the hazards similar to the HAZOP team. But, it generated a large number of unrealizable hazardous consequences compared to the team, due to the strict qualitative reasoning approach implemented. In order to filter and rank the results from HAZOPExpert using additional quantitative knowledge similar to the team, a semi-quantitative reasoning methodology is developed using the quantitative design and operating specifications of the process units, and process material property values. Significant reduction in the number of consequences was obtained using this approach on an ethylene plant case study.

Digraph-based models for automated HAZOP analysis

Hazard and operability (HAZOP) analysis is a systematic hazard identification procedure for predicting the various adverse consequences that might arise in a chemical plant due to abnormal causes. HAZOP analysis is typically performed by a group of experts by systematically considering all possible deviations from normal behavior of a process plant. This is a labor- and knowledge-intensive problem that can benefit from automation. Towards that goal, a framework using digraph-based models is described in this paper. The HAZOP-digraph models of the process units are developed in a process independent manner so that they can be used in a wide variety of process flowsheets. Based on this framework, an expert system for performing HAZOP analysis has been implemented in an object-oriented architecture using the expert system shell G2. A graphical HAZOP-Digraph model building tool is provided to let the user develop new models or add more knowledge to the existing models of the process units. The performance of this system was evaluated on an industrial HAZOP case study of a sour water stripping plant. The salient features of the expert system and its performance for this case study are described.