Oxygen is present in the environment as well as in natural gas streams. Natural gas, liquefied petroleum gas (LPG) and liquefied natural gas (LNG) contain some amount of oxygen in free natural form. Oxygen is contained in the vacuum system consisting of landfill and oil recovery systems and coal mines. Many pipeline specifications require natural gas to contain less than 10 parts per million of oxygen. Oxygen may get added or introduced in the process of being used in gas dryers. LPG blending includes processing with air to be able to reduce its calorific value and achieve air balancing. Landfill gas contains oxygen which enters the landfill as the landfill gas is withdrawn.
Requirements for Oxygen Removal
The presence of oxygen in natural gas is hazardous as it can cause the corrosion of processing machinery and increase the cost of maintenance and replacements. Furthermore, oxygen reacts with hydrogen sulfide to form sulfur. Oxygen also forms the oxidation of glycol solvents used in drying plants or creates salt in acid gas removal systems and affect the purge streams.
Oxygen is difficult to separate from natural gas. Not only is the technology not available and developed, but the market opportunities are perceived to be limited. Coupled with the high cost of such a removal project and a lack of sufficient avenues, the industry is yet to develop expertise and competence.
Natural Gas BTU Rating
The quickly increasing energy costs are pushing industry to actively pursue landfill gas recovery projects to produce BTU (British Thermal Unit is a traditional unit of measurement of thermal energy) gas to be supplied through the pipeline. This is becoming an attractive proposition even without the subsidies and tax breaks. There is no single process that is able to achieve the desired result of achieving a high BTU with 900+ BTU per cubic feet heating value.
Recovery of Landfill Gas
The technical risks and costs associated with the recovery of landfill gas are far greater due to the high operational and maintenance costs of machinery and equipment. However, the revenue that is earned from the recovered energy is a attractive profit and makes it a beneficial proposition. Currently, a few companies are offering catalyst-based systems as well as other processes to remove oxygen from natural gas. The X-O2™ system patented by Newpoint Gas Company uses a skid-mounted system to remove oxygen from natural gas.
Molecular Gate or Sieve Process
Engelhard Corporation has introduced a molecular gate or sieve process wherein the sieve contains pores of the exact size as that of the molecules of the various gases which enable it to separate the gases. This is a new technology which is yet to be perfected. The cost of this new technology is also quite high creating an entry barrier to adaptation.
A U.S. patent application titled "Oxygen Removal" by Raymond Anthony and team defines a process for the removal of oxygen. A hydrocarbon gas stream is allowed to pass over a material comprising of metals, including nickel, cobalt, copper, iron and silver, which causes the oxygen present in the gas to react with the metals.
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