(234c) An Innovative Approach: Integrated Amine Gas-Sweetening, Claus Sulfur Recovery, and Tail Gas Clean-up

Energy is the most important industrial, economical, and dynamic commodity in the world today. For many years and up till this day, natural gas has been one of the greatest sources of energy and is therefore a crucial factor in keeping the world in tact. Unfortunately, usable gas usually does not present itself in a ready-to-use manner, but must be treated. One of the biggest problems with ?fresh? gas is that it contains H₂S at high concentrations, which makes it unsatisfactory for use. This sour gas must be treated, and the environmentally hazardous H₂S that is removed must also be processed, where Sulfur can be isolated, collected, and sold. To achieve this, conventional gas-sweetening and Claus Sulfur recovery has been commonly used in industry and has proven to be the most efficient method thus far. The products recovered are sweet gas, an energy source, and Sulfur, which is an element used in many areas such as acid production, the advancement of computers screens, plastics, and even integrated with asphalt to form better roadways. Sulfur is gradually playing a greater role in the research of new technology and its popularity among chemical engineers in research, development, and industry is growing. With this project, the goal is to enrich the world's energy supply (with natural gas) and supply the market with an element that masks many hidden advantages (Sulfur), all while keeping the earth environmentally sound. Specifically, the objective is to treat 1420 MMSCFD of sour gas so that the H₂S concentration is brought down to 4 ppmv or 0.25 grains per 100 SCF of sweet gas. This was accomplished by designing a gas-sweetening amine unit integrated with a Claus process Sulfur recovery unit, along with tail gas clean-up. The sour gas was scrubbed from the feed gas in an absorber by an amine (MDEA). The rich amine was recovered in the regenerator and recycled back to the absorber. The choice of MDEA as the sweetening amine proved to be greatly beneficial because its selectivity towards H₂S was high, and degradation and corrosion problems are expected to be minute if present at all. In the SRU, the sour gas is combusted with excess oxygen to produce gaseous Sulfur and other byproducts. The effluent gases are cooled in order to obtain the Sulfur. Instead of the conventional third Claus reactor and incinerator, which is used to combust excess H₂S into SO₂, and later purge into the atmosphere, mole sieves were used (a stand-by incinerator is installed in case of upset reactions). The stream containing the excess H₂S that would normally enter the incinerator is passed through the mole sieves where the H₂S is collected. Once the catalyst is saturated with the acid gas, a small stream of the sweet sales gas is passed through the mole sieves to regenerate the catalyst, and the product sour gas is fed back into the gas sweetening system. In addition, any lingering traces of SO₂ leaving the reactors that would normally be purged are collected and recycled back to the first reactor where they are used in Sulfur production. These modifications ensure that absolutely no SO₂ is given off to the atmosphere and the maximum amount of Sulfur is recovered, resulting in a process that boasts a high degree of cost-effectiveness as well as never before reached environmental standards. In addition to the mole sieves, the implementation of various specially designed control elements makes this project unique. For instance, the mole sieves are run based on the swing mechanism, which means that as one tower absorbs the H₂S, the other tower is being regenerated, and then they switch. This ensures that there is no shut down of the mole sieves, which is efficient, both monetarily and time-wise. Furthermore, temperature sensors are installed in the walls of the reactors of the Claus Process. If the temperature, which represents the SO₂ concentration in the reactor is higher than the desired set point, the combustion rate and therefore SO₂ concentration is decreased. This action protects the walls and inside lining of the reactors. With these modifications made to the system e.g. mole sieves and control schemes, this project truly embodies innovation, creativity, and dynamic progression, which are chief components of any successful venture. Moreover, the fact that no Sulfur is lost by burning and purging SO₂, the performance of this system approaches ideality. This project has set global environmental standards by not emitting any SO₂ or H₂S, which are highly toxic gases whose effects range from bodily irritation to death. Overall, the main components of the gas-sweetening sweetening portion of the system are an absorber, a regenerator, and a heat exchanger (3 trains). The SRU consists of a furnace, two catalytic reactors (in series), two condensers, molecular sieves, and an emergency flare. The gas-sweetening plant was simulated by using a steady-state simulation package, HYSYS. All values obtained were compared to those of surrounding industries and were deemed reasonable. A private Excel-based program was used for the Claus Process balances. The SRU was simulated by using a SRU focused DOS program, TSWEET. Many outcomes were deduced from the project. Production-wise, 1415 MM scfd of sweet gas and 998 tons of elemental Sulfur were obtained daily. Moreover, the implementation of the mole sieves was also advantageous in that there was no pollution, the purchase cost is less since the inputs to the mole sieves are products of the amine plant, while the outlets of the mole sieves were fed to the amine plant, and the maximum amount of sulfur is recovered. Furthermore, the excess SO₂ streams released from the reactors were mixed together and recycled back to the first reactor where it was used in Sulfur production. Economically, the expected revenue was 45 M USD per annum and based on a fixed capital investment of 252 M USD, the payback period was found to be 5 and a half years. Therefore, economically, environmentally, and industrially, this plant is not only feasible but deemed to be a wise investment.