Progress of natural gas desulfurization technology

1 Common natural gas desulfurization methods

From the perspective of the development trend of natural gas desulfurization technology, catalysis, adsorption and biological desulfurization are relatively advanced technologies, and according to the current domestic and foreign natural gas desulfurization methods, it can be roughly divided into chemical desulfurization, physical desulfurization, biological desulfurization and new desulfurization methods.

1.1 Chemical desulfurization method

Chemical desulphurization can be divided into wet desulphurization and dry desulphurization [1]. Dry desulphurization efficiency is high, desulfurizer generally can not be regenerated, suitable for low sulfur gas treatment, in the current industrial application is less. The absorption and regeneration methods of wet desulfurization solution can be divided into three types: chemical absorption method and REDOX method. Wet desulphurization has large processing capacity and continuous operation, and is suitable for occasions with large natural gas processing capacity and high hydrogen sulfide content.

1.1.1 Wet desulfurization technology

Wet desulfurization is through the gas-liquid two-phase contact, the H2S in the gas is transferred to the liquid phase, so as to obtain the gas purification, and then the desulfurization liquid is recycled and recycled. Among them, the commonly used wet desulphurization includes catalytic oxidation method and alkamine method [2], among which the most widely used in the world is the alkamine method.

1.1.1.1 PDS desulfurization

As a new liquid phase catalytic oxidation desulfurization process, PDS technology has the characteristics of simple process, low cost and high desulfurization efficiency compared with other similar technologies, and can not only remove inorganic sulfur, but also remove organic sulfur. High catalytic activity, less dosage, wide range of desulfurization application; It produces more sulfur foam, is easy to separate, does not clog equipment, and is suitable for desulfurization of various gases and low viscosity liquids.

The working principle of PDS desulphurization technology is similar to that of liquid phase catalytic oxidation, but there are essential differences. It is the same that the whole process is composed of two sub-processes of catalytic chemical absorption and catalytic oxidation of sulfide; The difference is that PDS desulfurization technology has catalytic effect on both sub-processes, and desulfurization is the control step of the whole process, that is, PDS desulfurization technology changes the control step of the whole process from the general liquid phase catalytic oxidation regeneration process to the control step of the whole process.

PDS desulfurization is carried out under alkaline conditions, and the desulfurization solution is composed of PDS, alkaline substance and cocatalyst. The alkaline substance used is ammonia or soda ash, but from the point of view of equipment corrosion and removal of organic sulfur, ammonia is better than soda ash. PDS desulfurization technology should be used under the conditions that the operating pressure is not too high, the maximum is not more than 3.0MPa, and the atmospheric pressure is the best, because the high power consumption caused by high pressure natural gas desulfurization treatment is not ideal. In recent years, the PDS desulfurization technology has been continuously improved and perfected, and the performance of various aspects of the catalyst has been greatly improved and improved, and the development of PTS-4, PTS-200 has been developed to the current PTS-400. The improved PDS-400 does not require pre-activation or cocatalyst for industrial use, and the activity index is increased from 0.02minI1 to 0.04min or even above 0.06min, and the catalytic activity and selectivity are improved.

1.1.1.2 Aldoamine method

The alkamine process is the most commonly used method in natural gas desulfurization. The alkylamine process is a process in which H2S and CO2 in natural gas are absorbed by desulfurizing solution such as methyldiethanolamine and diethanolamine, and then react with the alkylamine solution [3]. The common desulfurizers are monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diethylene glycol amine (DGA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA). The hydroxyl group and amino group are contained in the structure of alcoholamine, and the hydroxyl group can reduce the vapor pressure of the compound and increase the solubility of the compound in water. The amino group makes the aqueous solution of the compound alkaline in order to promote its absorption of the acidic components.

MEA is the most alkaline among various amines, reacts most quickly with acid gas, can remove both H2S and CO2, and has no selectivity for these two acidic substances. MEA is able to purify H2S and CO2 up to several ppm, but regeneration requires considerable heat. If the raw gas contains COS, MEA method is not suitable due to irreversible reaction and final degradation of solvent.

DEA can remove both H2S and CO2, and is non-selective. Unlike MEA, DEA can be used in situations where COS is present in the feed gas. Even though the molecular weight of DEA is higher, its application is still economical because it can adapt to more than twice the load of MEA. The residual acid gas concentration of DEA solution after regeneration is much lower than that of MEA solution.