Originally developed to remove sulfur compounds from coke-oven gas, Connelly-GPM, Inc. Iron Sponge is now used around the world to treat natural gas, sewer gas, landfill gas, methane manufactured from biogas digesters, and a variety of other air and gas sources.
This product called Iron Sponge is hydrated iron oxide on a carrier of wood shavings and chips. Iron Sponge is most frequently supplied with 15 pounds of iron oxide per bushel of product.
Iron Sponge, which has been used for many years to treat other gas streams, is a very simple way to remove the corrosive, bad smelling H2S. It works to effectively remove the sulfide from the gas stream by forming stable iron sulfide, a solid.
This simple process is effective for high-pressure natural gas applications, low-pressure systems, and sewerage gas from anaerobic digestion of sewer sludge.
Uses and Processes
A new use for this process is treating the gas produced by landfills. This landfill gas, or biogas, is similar in composition to sewerage gas. After purification, this can be used as fuel or flared without the problem of SO2 in the exhaust.
The purification process consists of down flow gas through a packed bed of Iron Sponge, with the iron oxide reacting with H2S to produce iron sulfide and water. The water moves down through the bed with the gas and should be drained off to prevent accumulation. If mercaptans, the malodorous sulfur compounds in some gas streams, are present, they are also removed by Iron Sponge.
For Iron Sponge to effectively perform, it must be maintained within a range of moisture levels. This requirement is usually satisfied if the gas is saturated with water vapor, as is frequently the case. If not, a simple water spray will correct it. An excess of water is tolerated very well by Iron Sponge as long as the excess is drained off, so as not to flood the bed. Also, the reaction of iron oxide with H2S produces water, contributing to proper hydration.
Monitoring the drip water is an easy way to check the moisture level, pH, and reactivity. Since the iron oxide is impregnated into the wood surface, it will not wash off or migrate with the gas. If Iron Sponge has dried in storage it can be re-wet and still be effective.
To minimize downstream corrosion problems caused by H2S, the process should be located as close to the source of gas as possible. The process should be after a gas/liquid separator and before the dehydration process. The maximum temperature should not exceed 120°F. The minimum temperature is 50°F, or whatever is necessary to avoid hydrate formation for the system pressure and composition of the gas.
The Iron Sponge reaction is not pressure sensitive and is not affected by other gas constituents. Liquid hydrocarbons, however, should be effectively separated and removed before Iron Sponge treatment.
Iron Sponge Treatment and Equipment
The equipment needed for Iron Sponge treatment consists of a vertical vessel (of at least 8 feet of straight side for high pressure service, or 5 feet for low pressure service), which is filled with Iron Sponge. The gas is passed down flow with the H2S removed to meet pipeline requirements until the Iron Sponge is exhausted. Then it is either revivified or replaced.
Most installations can effectively operate on a single bed. If continuous operation is desired, then an alternate vessel and piping is needed to operate without interruption. Valves can be arranged so either bed can operate while the other is serviced.
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