DEMERUS NG: Natural gas Treatment
TECHNOLOGY OF LNG TREATMENT FROM MERCAPTANS (process “DEMERUS NG”)
The technology is used for deep treatment of natural gas from mercaptans.
Absorption of mercaptans contained in raw materials with an alkaline solution, followed by alkali regeneration in the presence of a heterogeneous catalyst.
Mercaptan sulfur in natural gas before treatment is maximum 0.400% wt., the residual content of mercaptan sulfur is not more than 0.0005% wt. The content of total sulfur in purified natural gas is not more than 0.0010% wt.
Schematic diagram of natural gas treatment from mercaptans:
Natural gas for treatment is supplied to the cube of the plate column absorber T-101. From the D-103 disulfide settler, the regenerated NaOH solution is fed to the upper plate of the T-101 absorber. When raw materials interact with an alkaline absorbent, chemisorption of mercaptans occurs with the formation of hydrocarbon-insoluble sodium mercaptide according to the reversible reaction (1):
RSH + NaOH = RSNa + H2O (1)
Treated from mercaptans, natural gas is sent to the D-101 separator to be separated from the entrained alkaline solution and then removed from the plant.
The alkaline solution saturated with mercaptides is removed from the T-101 absorber cube, heated in the E-101 heat exchanger to 50-70ºС and enters the R-101 regenerator cube. The calculated amount of air under pressure of 0.5-0.7 MPa is also supplied to the cube of the regenerator. In the R-101 regenerator, on the surface of the heterogeneous catalyst, alkali is regenerated according to reactions (2) and (3):
2RSNa + 0.5 O2 + H2O → RSSR + 2NaOH (2)
2RSNa + 1.5 O2 + H2O → RSО2SR+ 2NaOH (3)
The mixture of exhaust air, regenerated alkaline solution and formed disulfides from the top of the R-101 regenerator enters the D-102 separator. The air is removed from the top of the D-102 separator through a mist eliminator and is directed to the furnace for combustion.
The regenerated alkali solution with disulfides is withdrawn from the D-102 separator bottom, mixed with the gasoline fraction by pump Р-101А/В, cooled down to 40°С in the E-102 refrigerator and enters the D-103 disulfide sump.
The gasoline fraction saturated with disulfides is removed from the top of D-103 to the feedstock of catalytic cracking units, AVT or to hydrotreatment. The regenerated alkali solution from the bottom of the D-103 settler is returned to the T-101 absorber for natural gas treatment from mercaptans.
The technology increases the period of use of the alkaline solution without replacement up to 1 year, which makes it possible to reduce the consumption of alkali and the volume of alkaline effluents.
The heterogeneous catalyst provides strong retention of catalytically active components on the polymer carrier, increased resistance to catalytic poisons and thermal effects, and stable activity throughout the entire period of commercial operation. There is no need for its periodic or continuous replenishment with expensive compounds of metals of variable valence, which eliminates the ingress of cobalt phthalocyanines and their derivatives, as well as salts of other heavy metals into the wastewater of the enterprise. The warranty period of the catalyst is 8 years.