GB2217728A - Making synthesis gas - Google Patents

Abstract

In a reactor for producing H2/CO gas mixtures carbonaceous fuel is steam reformed in catalytic tubes and the partially reformed mixture is fed from the tubes into an annular catalytic zone into which oxidant is fed and where combustion and further reforming takes place to provide heat to the catalytic tubes which are located within the same pressure shell as the annular zone. Back flow of the gas from the tubes is prevented by means of a tubesheet attached to the inner wall of the catalyst annular zone, which tubesheet also supports the catalytic tubes.

Description

COMBINED REFORMER This invention relates to a reformer for carbonaceous gases and liquids in which they are reformed to gases containing carbon monoxide and hydrogen. It is an improvement on the reformers known as tubular steam reformers, incorporating therein an autothermic oxidation process.

The invention is a combined tubular primary and autothermal secondary reformer where the heat from the oxidation of part of the partially reformed feedstock is used to pre-heat and partially reform at least part of a carbonaceous gas or liquid such as natural gas or LPG. Normally the carbonaceous fuel will be mixed with steam prior to it entering the reactor.

The invention combines the principles of tubular steam reforming, partial combustion, adiabatic steam reforming and the use of the reformed product gas to provide heat for the tubular reforming of at least part of-the feedstock carbonaceous material.

There now follows a description of an embodiment of the invention.

Steam and a hydrocarbon are pre-heated externally to the combined reformer. The hot gas is then introduced into the bottom of reformer tubes located centrally in the refractory line combined reformer. The hot gas rises up the catalyst filled tubes. These are heated on the.outside by a descending gas stream from an adiabatic steam reforming stage. The catalyst in the tubes may be a conventional nickel based reforming catalyst of the appropriate type for the feedstock being reformed. The steam to carbon molar ratio will vary from 0.5 - 1 to 7 - 1, more preferably from 1.5 - 1 to 4.5 - 1, and most preferably in the range of 2 - 1 to 2.5 - 1. At the entry to the tube the feed is at a temperature of between 300 and 700 degrees C. more preferably 500 to 600 degrees C.The operating pressure may be in the range of 5 to 100 bar, more preferably in the range of 10 to 70 bar and most preferably in the range of 25 to 55 bar.

The gas flowing up the tubes is partially reformed into a gas containing carbon monoxide and hydrogen. This partially reformed gas leaves the catalyst in the tubes just above where the hot heating gas first meets the tube. Although it is possible to utilise catalyst above this point, the top section (above this point) is preferably filled with a low pressure drop inert material. At the top of the tube a grid is used to hold the catalyst or low pressure drop material in the tubes so as to prevent the gas flow removing the catalyst or low pressure drop inert material from the tube.

The top part of the tubes are inside an anulus on the outside of which is a bed of catalyst.

After leaving the top of the tubes, the partially reformed gas enters the top of an outer anular space. In this space the oxidant is introduced and the gas is partially combusted. The oxidant is an-oxygen containing gas. It may be air or it may be oxygen combined with steam. It may also contain carbon dioxide.

The reaction between the oxygen and the gases present raises the temperature and provides heat for the subsequent adiabatic reforming process catalysed by catalyst.

The hot gas then flows down through an anular bed of catalyst where adiabatic reforming takes place. The temperature falls until the reactants come close to equilibrium. The gas is now at a temperature of 600 to 1200 degrees C., more preferably 700 to 1100 degrees C. and most preferably 800 to 1000 degrees C.

On leaving the anular catalyst bed the gases flow around the outside of the reformer tubes and eventually leave the base of the reactor at a temperature below that which they leave the anular catalyst bed.

Using this invention it is possible to introduce additional partially reformed gas from another reactor system. This additional partially reformed gas may be added to the gas leaving the reformer tubes. The effect of this is to reduce the quantity of oxidant required.

The oxidant may be introduced into the reactor below the surface of the anular catalyst bed and combustion, and further reforming then occurs simultaneously as the gas flows through the anular catalyst bed. A special type of catalyst, preferably containing a precious metal may be used in this embodiment of the invention.

An advantage of this simultaneous combustion and reforming is to reduce the peak temperature of the reactor. The invention may be arranged such that the peak temperature occurs close to the outlet from the anular catalyst bed.

Figure 1 shows two embodiments of the invention, in Figure 1A the oxidant enters the reactor above the anular catalyst bed.

In Figure 1B the oxidant enters the reactor within the anular catalyst bed.

The following is an example in which the oxidant is air and the carbanaceous fuel is mainly natural gas to which steam and a small amount of hydrogen has been added. The same material balance given below is obtained whether or not catalytic reforming is used.

Flows Kg mol/h Feed Gas Oxidant Partially Gas Ex Reformed Combined Gas Reformer Hydrogen 3 119.3 252.3 Carbon Monoxide - 9.3 70.5 Carbon Dioxide - 24.9 37.2 Methane 90 75.8 2.3 Nitrogen 1 200 1.0 201.0 Ethane 7 Propane 2 Steam 250 Oxygen 50 191.0 205.1 Total 353 250 421.3 768.4 Temperature OC 550 550 681 954 Pressure Kg/cm a 33 33 30.5 30 954 C is the temperature of the gas leaving the anular catalyst bed. 6810C is the temperature of the gases leaving the tubes just prior to reacting with the oxidant.

In this example the heat exchange between the hot gas leaving the anular catalyst bed and the gas in the tube is 2.0 gigacals per hour. Between six and ten tubes are required for the above material balance. The tubes having diameters of circa 100 mm.

The tube diameter might vary between 90 and 160 mm depending upon the activity of the catalyst used. Tube length would be approximately 12 metres. But again it could vary from 10 to 15 metres depending upon the activity of the catalyst used.

In other words this invention is a reactor in which heat produced from reaction between an oxidant and a carbonaceous gas firstly is partly used to cause more of the carbonaceous gas to be reformed in an anular space and then is at least partly used to provide heat to tubes containing reforming catalyst located within the same pressure shell as the oxidant reaction stage and where back flow of the gas from the tubes is prevented by means of a tubesheet attached to the inner wall of the catalyst anular space, which tubesheet also supports the reforming tube.

The reactor may be arranged as that the reactants flow upward through the tubes and downward through the anular bed before giving up some of their heat to the reformer tube bundle.

Claims (1)

1. CLAIM 1 A reactor in which heat produced from reaction between an oxidant and a carbonaceous gas firstly is partly used to cause more of the carbonaceous gas to be reformed in an anular space and then is at least partly used to provide heat to tubes containing reforming catalyst located within the same pressure shell as the oxidant reaction stage and where back flow of the gas from the tubes is prevented by means of a tubesheet attached to the inner wall of the catalyst anular space, which tubesheet also supports the reforming tube.

   CLAIM 2 A reactor as claimed in Claim 1 wherein the reactants flow upward through the tubes and downward through the anular bed before giving up some of their heat to the reformer tube bundle.