Contaminant hydrogen sulphide

To prepare gas for evacuation it is necessary to separate the gas and liquid phases and extract or inhibit any components in the gas which are likely to cause pipeline corrosion or blockage. Components which can cause difficulties are water vapour (corrosion, hydrates), heavy hydrocarbons (2-phase flow or wax deposition in pipelines), and contaminants such as carbon dioxide (corrosion) and hydrogen sulphide (corrosion, toxicity). In the case of associated gas, if there is no gas market, gas may have to be flared or re-injected. If significant volumes of associated gas are available it may be worthwhile to extract natural gas liquids (NGLs) before flaring or reinjection. Gas may also have to be treated for gas lifting or for use as a fuel. 

The most common contaminants in produced gas are carbon dioxide (COj) and hydrogen sulphide (HjS). Both can combine with free water to cause corrosion and H2S is extremely toxic even in very small amounts (less than 0.01% volume can be fatal if inhaled). Because of the equipment required, extraction is performed onshore whenever possible, and providing gas is dehydrated, most pipeline corrosion problems can be avoided. However, if third party pipelines are used it may be necessary to perform some extraction on site prior to evacuation to meet pipeline owner specifications. Extraction of CO2 and H2S is normally performed by absorption in contact towers like those used for dehydration, though other solvents are used instead of glycol. 

In electrochemical cells sample oxidation produces an electric current proportional to the concentration of test substance. Sometimes interferences by other contaminants can be problematic and in general the method is poorer than IR. Portable and static instruments based on this method are available for specific chemicals, e.g. carbon monoxide, chlorine, hydrogen sulphide. 

Neutralization of strong mineral acids from metal finishing trades (sulphide and hypochlorite contamination common) Fierce reaction Possibility of mixing with water or organic materials Chlorine Nitrogen dioxide Sulphur dioxide Hydrogen sulphide... 

Hydrogen sulphide and sulphur dioxide are also usually the result of pollution sometimes they are produced by the interaction of two contaminants, but sometimes bacterial action may be contributory. Both gases may initiate or accelerate corrosion of most metals. 

In sea-water systems such attack may occur under dead barnacles or shellfish, the decomposing organic matter assisting corrosion. Pitting is most likely to occur in polluted in-shore waters, particularly when hydrogen sulphide is present. In such contaminated waters non-protective sulphide scales are formed and these tend to stimulate attack. 

Some bacteria can give products a rancid smell others can impart the "sweet" odour of dirty drains by the production of certain pyrazine derivatives. Other bacteria, known as sulphate reducers, for example Desulphovibrio desulphuricans, are able, under anaerobic conditions, to utilise oxygen from sulphates leading ultimately to the formation of hydrogen sulphide. Opperman and Goll (1984) in their study of contaminated emulsion paints concluded that more than a quarter were infected with these and other anaerobic organisms. 

Most bore waters include high concentrations of at least one of the following chemical contaminants (Table 1) lithium (Li), boron (B as H3BO3), arsenic (As), hydrogen sulphide (H2S), mercury (Hg), and sometimes ammonia (NH3). If released into a river or lake, these contaminants can potentially damage aquatic life, terrestrial plants, and/or human health. The disposal of highly saline bore waters can also have an adverse effect on water quality. 

Off-gas from the coke burner ( -Gas) contains nitrogen, sulphur dioxide (SO2), hydrogen sulphide (H2S), carbon monoxide (CO), carbon dioxide (CO2), water vapour and other trace contaminants. The -Gas is directed to the CO Boiler for incineration where sulphur compounds are converted to SO2. The Boiler flue gas is passed through electrostatic precipitators for particulate control and then emission to atmosphere. The CO Boiler also serves as the Sulphur Plant tail gas incinerator. Maximum sulphur emissions are 146 tonnes/day or 10.6% of sulphur contained in bitumen feed to the cokers. 

It is probable that the inconstancy of the results obtained by various investigators for the specific gravity and other characteristics of y-sulphur is due to contamination of the substance examined with other forms of sulphur or with foreign substances. Such a probability is increased by the description of a hydrated form of amorphous sulphur the composition of which points to its being a definite hydrate, S8.H20 this compound is stated to be obtainable by the interaction of hydrogen sulphide and sulphurous acid in aqueous solution.5... 

Aqueous solutions of alkali chromates yield with hydrogen sulphide a precipitate of chromium hydroxide contaminated with sulphur, whilst alkali sulphide, polysulphide, thiosulphate and colloidal sulphur remain in the solution.3... 

Commercial phosphorus often contains a small quantity of arsenic. This on the treatment with nitric acid is oxidized to arsenic acid, which would contaminate the preparation of phosphoric acid unless removed by hydrogen sulphide. 

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