Boosting Gas Processing Energy Efficiency by Waste Heat Recovery

A continual improvement in energy efficiency of existing plants is imperative to achieve ADNOC target to reduce greenhouse gas emissions (GHG) intensity of operations by 25% in year 2030. The waste heat recovery (WHR) from incinerator stacks of existing Sulphur Recovery Units (SRUs) in ADNOC Gas Processing exhibits a substantial potential & contributor of energy savings and emission abatement. A high level assessment was carried out for various heat sources, results showed substantial WHR potential can be availed from SRUs. Consequently, a feasibility study was carried out to evaluate several options to recover energy from incinerator stacks of existing Sulphur Recovery Units (SRUs). The feasibility study addressed three options of recovering energy from SRUs incinerator stack exhaust; generating saturated steam, generating power and combined solution of steam & power. Those options were assessed in terms of technical feasibility and commercial viability. The study indicated that steam generation by HRSGs is technically viable and economically feasible, and considered as the best option for WHR from the existing SRU Incinerator Stacks. The WHR benefits that can be realized from just one incinerator stack by recovering the waste heat and reducing the flue gas temperature by 400 °C only (from 700 to 300 °C) are: More than 80 TPH saturated HP steam generationFuel gas savings and corresponding monetary benefitsSignificant abatement in GHG emissions The study revealed that WHR does not pose acid condensation risk due to the safe margin between the acid dew point and the actual flue gas temperature. The study also established that other constraints like pressure drop, space, tie-in location and emissions dispersion are not the showstoppers.

Exergy analysis and performance study for sour water stripper units, amine regenerator units and a Sulphur recovery unit of a refining plant

A refining column in the middle east that started its official production in 2020 provides its sour wastewater from all refinery plants to two sour water units (SWS1 and SWS2) to strip H2S and NH3. Sour gas from the refinery uses a lean amine solution for gas sweetening to absorb H2S in different absorbers. Rich amine with H2S is then stripped in two amine regeneration units (ARU1 and ARU2). The overhead of SWS and ARU units provide the acid gas feed to the sulphur recovery unit (SRU) to produce sulphur and prevent any acidic emissions against environmental regulations. First, the SWS1 unit is simulated using Aspen HYSYS V.11. A complete exergy study is conducted in the unit. Exergy destruction, exergy efficiency and percentage share in the destruction are calculated for all equipment. The highest exergy destruction rate was in the stripper with 5028.58 kW and a percentage share of 81.94% of the total destruction. A comparison was conducted between the exergy results of this study with two other exergy studies performed in the same refinery plant. The columns in the three studies showed the highest destruction rates exceeding 78% of the total destruction of each unit. The air coolers showed the second-highest destruction rates in their units with a percentage share exceeding 7% of the total destruction. The pumps showed the lowest destruction rates with values of less than 1% of the total destruction of each unit. Then, an individual simulation is conducted for stripper1 of SWS1, stripper2 for SWS2, regenerator1 of ARU1 and regenerator2 of ARU2. The individual simulations are combined in one simulation named combined simulation to compute the composition of acid gas from SWS and ARU units feeding SRU. Then, the SRU unit is simulated via a special package in HYSYS V.11 named SULSIM. The computed composition from SWS and ARU is exported to excel where it is linked with SRU simulation to calculate sulphur production. For the first time in any article in the world, all data feeding SWS, ARU, and SRU units are connected to a live system named Process Historian Database (PHD) to gather live data from the plant and perform plant optimization.

Performance Assessment of a Sulphur Recovery Unit

A refinery plant in the middle east started its official production in 2020. All the refinery plant acidic gas is fed to the Sulphur recovery unit plant to produce sulphur and prevent any acidic emissions against environmental regulations. The Sulphur recovery unit was simulated via special package named SULSIM. The results were validated, then the simulation was used in case studies to understand some important parameters of Sulphur recovery plants. The effect of decreasing the combustion air inlet temperature, the effect of decreasing the Claus reactor 1 inlet temperature and the effect of decreasing the thermal reactor feed were studied. Decreasing combustion air outlet temperature on the thermal reactor decreases the thermal reactor burning temperature, increases the concentration of COS and CS 2 by-products. Decreasing Catalytic reactor 1 inlet temperature decreases the hydrolysis reactions of COS and CS 2 but increases the Sulphur conversion efficiency. Decreasing AAG feed to the thermal reactor decreases the waste heat boiler duty.

Computational Fluid Dynamics-Based Efficiency Evaluation of Ammonia Containing Gas Combustion in the Claus Reaction Furnaces

Based on the computational fluid dynamics method using ANSYS Fluent software, we carried out a simulation of acid gases combustion process in the Claus furnaces with further combustion of ammonia containing gas originated from sour water stripper. The sulphur recovery unit of the heavy residue conversion complex owned by TAIF-NK was considered as a research subject. As per the results of CFD-simulation, the optional scenarios were defined for utilization of ammonia containing acid gases in the sulphur recovery unit by adjustment of gas composition, thermodynamic conditions, as well as by controlling the flow pattern in the Furnace. The data obtained agree quite well with the actual performance parameters of the existing unit and the findings in the public domain.

Performance Monitoring of a Sulphur Recovery Unit: A Real Start- up Plant

A Sulphur recovery unit at a refining plant in the Middle East, which began official production in 2020, treats all acid gas to elemental Sulphur. Acid gas cannot be released into the atmosphere because of stringent environmental regulations. To test some essential parameters, the plant was simulated using a special Sulphur package in HYSYS called SULSIM. One of the most critical keys, the (H 2 S/SO 2 ) ratio, was checked after simulation validation. The optimal ratio is 2. Any deviation from this ratio results in serious issues in the process, such as catalyst ageing in the reactors. The effect of reducing the ratio from 2 to 0.22 was investigated in a case study. The temperature of the reduction reactor's outlet rose from 279.73 o C to 314.34 o C, which was higher than normal. The performance of the catalyst was measured on six separate days. The temperature difference and the pressure difference through the bed are the two most important parameters in catalyst monitoring. The ΔT designs for the first Claus reactor, second Claus reactor, and Reduction reactor are 51, 20 and 24 o C, respectively. 0.04, 0.14, and 0.04 kg/cm 2 g are the ΔP designs in the first Claus reactor, second Claus reactor, and Reduction reactor, respectively. The actual parameters were found to be in the normal range. Sulphur production is calculated in two ways: by the level of the Sulphur production tank and by calculating the material balance by laboratory analysis. Based on a comparison in four days the calculations are precise because of the levels, and large deviations are revealed by laboratory analysis. The percentage deviation error was found to be (-36.4, 70.7, -7.6, -10.5) percent by the laboratory analysis.

Sulfidation Rate Prediction on Tube-to-Tubesheet Joints in a Waste Heat Boiler in a Sulphur Plant

Sulfidation corrosion of the carbon steel tubes at the tube-to-tubesheet joint often governs the life of waste heat boilers in sulphur recovery plants. Conventional tube joints typically have a welded joint located at the hot-side face of the tubesheet. An alternative design involves welding the tubesheet joint at the cold-side face of the tubesheet, close to the boiler feed water. The alternative design also employs stainless steel cladding on the tubesheet face and a tube-hole sleeve selectively at high-temperature locations. Finite element heat transfer analysis is used to establish the thermal profiles of the conventional and the alternative designs. From the worked example, the alternative design provided a lower metal temperature by approximately 80 °F at the joint, as compared to the conventional tube joint. Sulfidation rate prediction based on a sample gas composition using ASSET (Alloy Selection System for Elevated Temperatures) Software predicts that the alternative design can reduce the sulfidation rate by 35% because of the lower metal temperature.