Process for producing dry synthetic natural gas (SNG)

Abstract

A process for producing dry synthetic natural gas (SNG, Synthetic Natural Gas) from solid or liquid, carbonaceous fuel, substantially consisting of the following process steps: a) gasification of a solid or liquid, carbonaceous fuel to a raw synthesis gas b) cooling of the gas, separation of solids and the gas condensate c) raw gas conversion d) washing of the gas with methanol for separating hydrogen sulfide, carbon dioxide and moisture, wherein the methanol is circulated via a regeneration plant, e) methanation, f) condensation of moisture by means of cooling and/or cold water, g) further drying of the gas by condensation at low temperature by adding methanol to avoid the formation of ice.

Claims

1. A process for producing dry synthetic natural gas from solid or liquid, carbonaceous fuel, said process comprising the following process steps carried out in the following order: a) preparing a first gas by gasifying the fuel, wherein said first gas consists substantially of carbon monoxide, carbon dioxide, methane and hydrogen; b) preparing a second gas by cooling said first gas and separating from the first gas solids and a gas condensate; c) preparing a third gas by converting carbon monoxide in said second gas into carbon dioxide and hydrogen; d) preparing a fourth gas by separating hydrogen sulfide, carbon dioxide and steam from said third gas by washing the third gas with methanol as solvent, wherein the methanol is circulated via a regenerating means for separating hydrogen sulfide, carbon dioxide and water from the methanol, wherein the regenerating means also comprises a methanol-water separation column; e) preparing a fifth gas by catalytically-supported-conversion of the carbon monoxide, residual carbon dioxide and hydrogen in the fourth gas, wherein the fifth gas consists substantially of methane and steam; f) preparing a sixth gas by predrying the fifth gas by condensing moisture by means of cooling and/or cold water; g) preparing a seventh gas by adding methanol to the sixth gas; h) preparing an eighth gas by separating steam from the seventh gas and condensing out the steam by forming a water-methanol mixture; i) preparing a ninth gas by separating the water-methanol mixture from the eighth gas; and j) obtaining said dry synthetic natural gas by heating the ninth gas to a desired discharge temperature.

2. The process according to claim 1, wherein the water-methanol mixture separated in step i) is introduced into the regenerating means of step d) and treated in the methanol-water separation column.

Description

DESCRIPTION OF THE INVENTION

(1) It is the object of the invention to provide a process which avoids the disadvantages of the prior art. This object is solved by a process according to the features of claim 1.

(2) According to the invention, the prior art processes for removing the residual moisture by a condensation of the moisture at a low temperature corresponding to the targeted dew point, which are mentioned in process step g), are replaced. After having been predried in process step f) by condensing out the moisture by means of cooling and/or cold water, the gas is mixed with methanol, so that methanol is present in the gas in the form of vapor or aerosol. For this purpose, the methanol preferably is brought in contact with the gas by injection or spraying in. The gas then is passed through a condenser, wherein it is cooled to the desired dew point of below 0 C. The water condensed out along with the methanol distributed in the gas forms a liquid water-methanol solution. The formation of a water ice layer on the heat exchanger surface of the condenser is avoided in this way.

(3) The water-methanol solution is separated from the gas and the gas is heated to the desired discharge temperature, so that dried synthetic natural gas is obtained. In the process according to the invention it is advantageous that with the exception of methanol, which anyway is present due to its use in process step d), no further auxiliary substances foreign to the process, such as glycol or adsorbents, are required. The logistic expenditure for handling and keeping these auxiliary substances in stock therefore can be omitted.

(4) In an advantageous aspect of the invention the water-methanol solution separated from the water is charged for processing into the methanol-water separation column of the regeneration means of process step d). Due to the utilization of the separating apparatus present already, a particularly efficient procedure is obtained.

INDUSTRIAL APPLICABILITY

(5) With the invention, an economic and environmentally friendly process thus is provided for the treatment of raw gas produced by pressure gasification of solid, carbonaceous feedstocks, which provides for a higher energy efficiency with regard to the thermal energy contained in the raw gas and in the gas condensate.