Scavengers are technological options used to reduce the H2S levels in natural gas, when the stream to be treated is less than 100 MMCFD with H2S concentration up to 100 ppm. Laboratory and field tests have been performed in order to determine the reaction capabilities of such chemical treatments. Then, to establish the effect of liquid water on the solid and liquid H2S scavengers performance, laboratory tests were carried out, using different H2O/H2S ratios. The results obtained from these tests, indicated that a ratio of 0.024 g H2O/g H2S did not affect the absorption capability of the liquid H2S scavenger. Besides, the solid H2S scavenger had three zones of absorption capacity, which were functions of water content.
Natural gas produced in northern Venezuela has an H2S content of 25-80 ppm and the concentration of this contaminant must be reduced to 8 ppm to meet the marketing requirements. This goal can be achieved by using regenerable processes in contactor vessels1,2. However, if natural gas volume to be treated is about 60 ? 125 MMCFD and H2S content is lower than 100 ppm, non regenerable processes can be employed1,2.
Solid and liquid H2S scavengers are used in non regenerable processes and the reactions between the scavengers and the H2S are not reversible. Liquid H2S scavengers can be applied directly in the gas pipelines to treat a gas stream volume of 40-60 MMCFD, with an H2S concentration up to 100 ppm. Solid H2S scavengers are used in fixed beds to react with a gas flow up to 125 MMCFD, containing less than 100 ppm of H2S.
In order to study the H2S liquid and solid scavengers performance, laboratory and field tests have been performed, at the conditions of northern Venezuela gas streams3, 4. Different H2S liquid scavengers were tested in the 414 kPa (60 Psi) Muri-Muscar gas pipeline that transports 235030 m3/d (normal conditions), with an average concentration of CO2 and H2S of 8% and 40 ppm, respectively. According to the results obtained from these study, the H2S liquid scavengers had a good behavior, reducing the H2S concentration to 7 ppm.
In addition to the absorption capacity of the liquid scavengers, nitrogen residual was measured downstream to the injection point of the scavenger, considering most of the liquid H2S scavengers evaluated in this field test were triazine-based scavengers. As a result, a relation between residual nitrogen measured and the amount of scavenger applied was noted. Furthermore, scavenger residual and by-products formed during the scavenging process tended to diminish the corrosion rate of carbon steel.
Afterwards, the idea of applying these chemical treatments in gas pipelines transmitting natural gas with a water content of 907 g /MMCF (2 lb/MMCF), considered as dry gas stream, was explored in order to define strategies for optimizing the use of liquid H2S scavengers. Taking into account the possibility of treating dry natural gas streams, laboratory tests were done to observe the effect of water on the performance of an H2S liquid scavenger, by determining the absorption capacity and the characteristics of the by ? products formed in the scavenging reaction.
On the other hand, a solid H2S scavenger based on iron oxides was evaluated in an industrial scavenging process, using for this purpose an amount of 14 tons of the product. Considering the concentration of H2S in the gas stream to be treated is 25-30 ppm, the flow passing through the reactor, 22 MMCFD and the adsorption capacity of the solid scavenger is 0.16 g sulfur/g scavenger, the duration of this test was estimated in a range of 78-97 days.
The gas stream treated in the reactor during this industrial test is call
