The desulphurizing process consists of a fixed-bed or batch-type granular hydrogen sulfide reactant contained in a pressure vessel. The reactant in this case is one of the granular products. Both the unused and spent product are safe and stable. During the process, gas or vapor flows through the consistently sized and shaped granular product in the bed, chemically reacting with hydrogen sulphide to form a stable and safe byproduct. The process advantage is that product consumption is dependent only on the amount of hydrogen sulfide that passes through the bed. This economically matches the need for H2S removal with variations in system flow conditions and outlet specifications, regardless of the total volume or other common components of the gas. The flexibility of the process allows the system to adapt to variations in H2S outlet specifications that may result from changes in operating preferences or tighter regulations, often without additional capital equipment or system retrofitting. Predictable pressure drops, long bed life, easy and safe handling, and a simple reliable operation are a few of the features of the desulphurizing process.
Just upstream of the desulphurizing vessel(s), the installation requires a small inlet separator with a coalescing filter to remove excess liquids from the gas. Care should be taken to insulate the lines and the vessel(s) to prevent a temperature drop of no more than 5° F (–15° C) after the last liquid separator across the outlet of the vessel. The actual design of the vessel(s) can be customized to specific site needs based on inlet gas flow, operating pressure, desired pressure drop, and the days-to-outlet-H2S specification.Low predictable pressure drops, as low as a few inches of water, allow a wide range of reliable applications and equipment configurations. Properly constructed vessels should last 20 years or more. Site facilities should include the appropriate piping to and from the desulphurizing vessel and vessel support. Insulation of the piping and vessel may be required, depending upon the degree of atmospheric cooling anticipated. Optional equipment may include a water-spray system to saturate the inlet gas. System and internal vessel design specifications, and vessel fabrication and installation assistance is available from the CAVALCO OMG representative given site-specific information.
The most basic design is a single vessel where the inlet H2S concentration is reduced at the outlet to “nil” at the beginning of the bed life, gradually increasing to an outlet specification. Temporary bypass of the vessel or interruption of gas flow is necessary for the short time it takes to replace the granular material. The main advantage of this type of system is that the capital costs are minimized.
This arrangement is feasible as the quantities of H2S increase and for systems operating with sufficient working pressure (about one-third psig or more). Two vessels are arranged in series, flowing gas through the first bed into the second. The lead vessel acts as the “working” unit to remove all of the H2S at the beginning of a treatment period with its outlet H2S increasing over time. The gas can go to the second, or “lag” vessel for further polishing, or it can bypass the second vessel up to the desired gas H2S outlet specification. The operation of the lead bed is similar to the single-vessel arrangement. The second vessel can be placed in operation at startup, or it can be used to polish the H2S remaining in the gas from the lead vessel when the level of outlet H2S reaches the maximum specification. Once the lead vessel inlet and outlet concentration are equal, the material is considered spent or exhausted. The gas flow is then directed to the second vessel, while the spent material is removed from the lead unit. The second vessel becomes the lead or “working” unit with the new product bed (in the lead unit) operating as the lag or polishing unit — all without gas-flow interruption. The lead/ lag arrangement allows more efficient use of the granular material with no interruption in unit service and greater process reliability. When operating in this lead/lag mode, removal of the spent material can be conveniently scheduled using the days or weeks allowed during the change-out “window” — without exceeding maximum outlet H2S concentrations.
A CAVALCO OMG representative will assist you in determining the best option for implementing of the product choice and technology.