Plant for production of synthesis gas based on reforming, comprising one primary reformer and one secondary reformer, and a reformer feasible for use in the plant.

Area of invention

The present invention relates to a plant for the production of synthesis gas based on reforming, for the production of ammonia, methanol, GTL or other end products, where the plant comprise a primary reformer and a secondary reformer. The invention also relates to a reformer suitable for use as a primary reformer at the plant according to the invention, in addition to other uses.

Background and prior art of the invention

With the production of synthesis gas, which is a mixture of carbon monoxide and hydrogen, possibly containing carbon dioxide, and by further processing of the synthesis gas, a wide range of products can be produced, such as ammonia, methanol, GTL and other end products. GTL, gas to liquids is a common phrase for several processes where synthesis gas is processed, amongst others the Fischer-Tropsch process for production of diesel and paraffin. In particular for production of ammonia and methanol, but also the production of other products, one available technology is to use a primary reformer, which is an externally fuelled reactor tube (a conventional steam reformer) and a secondary reformer, which is internally fuelled by oxygen/air. All or part of the process gas is routed through catalyst filled reformer tubes inside the primary reformer and thereby becomes partially reformed, after which the partially reformed process gas is directed to the secondary reformer. This technology is commercially available by licensing from owners. Downstream for the secondary reformer a waste heat boiler will usually be located, followed by a superheater for heat recycling.

One of the problems with this prior technology is the transfer line between the primary and secondary reformer for the transfer of hot and partially reformed gas. The gas from the outlet of the primary reformer is collected into one or several collectors, either directly or through flexible pigtails. The transfer line is insulated with one or several layers of ceramic materials. The steel casing is flexible during heating and

cooling, but the insulation is rigid and brittle. This will result in that the insulation may crack open and hot gas will therefore have access to the steel casing. The transfer line is therefore a component requiring inspection and maintenance; and damage to the steel casing maintaining the pressure, may result in a significant halt of the operation. There is also a loss of heat and pressure inside the transfer line. The transfer line is typically shaped as a vertical line with a horizontal part, which links the collector with a horizontal part on top end of the inlet of the secondary reformer as illustrated in FIG. 3. The gas needs to change its streaming direction 90 degrees twice leading to some erosion to the insulation. The upper end of the secondary reformer is placed at a distance above the ground. The top part needs to be taken off for maintenance or inspection. A large crane is needed for this and in particular in wind exposed areas, this can be dangerous and lead to delays. If the superheater is installed on top of the waste heat boiler as a heat exchanger, the lifting of the entire assembly of equipment becomes a very difficult and critical operation. There is a demand for a reforming plant, which is advantageous in relation to the above-mentioned problems.

The commercialised available reformers have different arrangement of burners. One commercialised reformer has the fuelling on top of the device, resulting in the streaming direction of the hot exhaust gas is opposite to what is natural. There are prior reformers with fuelling from the bottom, meaning that the burners are placed at the bottom of a combustion chamber, but with a downward streaming direction for the processed gas. For all of the embodiments, the catalyst will be crushed both by gravitation, the dynamic pressure of the process gas streaming from top to bottom and the crimping of the reformer tubes by heating and cooling. At the bottom part of the reformer tubes, the catalyst is mostly exposed to crushing, due to both gravitation and the fact that the hottest parts of the tubes contract the most when the reformer is cooling during shut down. It is a demand for a reformer, which is more advantageous in relation to the above-mentioned problems.

The aim with the present invention is to provide a plant and a primary reformer, which meet the above-mentioned demands.

Summary of the invention

The present invention provides a plant for production of synthesis gas, based on reforming, for production of ammonia, methanol, GTL or other end products, comprising a primary reformer and a secondary reformer, distinguished in that the

connection from the primary reformer to the secondary reformer consists of a collector, the outlet from the primary reformer, in form of said collector with reformer tubes connected via optional pigtails, is at the same height level as the inlet of the secondary reformer; and both the primary and secondary reformers stand on a ground level with access for lifting and maintenance devices.

The term that the connection from the primary reformer to the secondary reformer consists of a collector, means that the connection is by the mentioned collector, without a so-called "transfer line".

In an advantageous form of operation the ground level is arranged as a terrace, where the primary reformer stands at a higher level than the secondary reformer. A further form of operation is that the secondary reformer is placed in a depression on ground level, at a lower level than the primary reformer. In an advantageous form of operation, the primary reformer is vertically turned (upside down) in comparison to what is typical amongst commercially available primary reformers. In the mentioned form of operation, the secondary reformer is arranged on a higher ground level than the primary reformer. The plant according to the invention provides a major simplification in relation to the operation, maintenance, inspection and repair in relation to prior known comparable plants.

The invention also provides for a reformer suitable for the use as a primary reformer at a plant according to the invention, together with other uses. The reformer is distinguished in that one or several burners are place at the bottom of a combustion chamber, reformer tubes with an inlet for processed gas at the bottom end and an outlet at the upper end extending up through the combustion chamber. The reformer tubes are connected by optional pigtails to a collector, which may be directly connected to an optional secondary reformer, exhaust gas from the burners flowing by natural convection to heat exchange in a convection section and the processed gas flowing in the natural direction of the convection. Other uses refer to the reformer may be used for conventional reforming without the additional oxygen fuelled secondary reformer, for instance in the form of a tube reformer for tubular steam reforming.

Illustrations

The present invention is illustrated by using figures, where: Fig 1 illustrates a reforming plant according to the invention,

Fig 2 illustrates a reforming plant according to the invention, Fig 3 illustrates a conventional reforming plant and therefore represents prior art and,

Fig 4 illustrates a reformer according to the invention.

Detailed description

Reference is made to Fig 1, which illustrates a reforming plant according to the invention. The plant comprises a primary reformer with an inlet for process gas in or at the upper end. The reformer tubes extend through the primary reformer and has an outlet at the bottom end of the primary reformer. The reformer tubes are connected to a collector by flexible connectors, so-called pigtails. The collectors are assembled with direct connection at the same height level as the secondary reformer, clearly illustrated by Fig 1. The secondary reformer has an inlet for 02/air and steam in or at the upper end. The secondary reformer has a waste heat boiler connected at the bottom end. According to Fig 1, the primary and secondary reformers are placed at different ground levels as the ground level is arranged as a terrace. There is no transfer line between the primary reformer and the secondary reformers.

Reference is further made to Fig 2, which illustrates a similar model of primary and secondary reformers and the connecting of the mentioned models solely by means of a collector. However, the embodiment as illustrated by Fig 2, shows that the secondary reformer and the connected waste heat boiler are arranged in a depression on the ground level.

A plant for the production of synthetic gas by reforming comprise of several more components for equipment than what is described here, but for the sake of simplicity, these are not further illustrated or described. Depending on the type of equipment assembled up-stream or down-stream for the illustrated equipment devices, the ground level may be arranged as terraces on several levels, or by elevating or by depression of the ground level, in order to simplify the connection and minimalize the length of the transfer lines and the numbers of connections. According to the invention, significant importance will be given to good access for lifting, inspection and maintenance and operational devices, regardless as to whether these devices are installed permanently at the plant or are assembled on vehicles.

Reference is further made to Fig 3, which illustrates a traditional embodiment of a primary and secondary reformer in combination, at a conventional plant. The

primary and secondary reformers are here placed on ground level in the same plan, and the primary reformer is connected to the secondary reformer by a transfer line, referred to as TL. There is no transfer line TL with the current invention.

Reference is further made to Fig 4, which illustrates a reformer according to the invention, where the reformer is usable as a primary reformer at a plant according to the invention, and a reformer used by itself, meaning without a secondary reformer, for instance in form of a tube reformer or a conventional reformer; or an autothermal reformer. More precisely, process gas is directed in to the bottom and led through the reformer tubes, by pigtails arranged at the top of the reformer tubes to a collector, which is arranged with direct connection to an externally placed secondary reformer. Combustion chambers with burners installed at the bottom are placed inside the primary reformer. The reformer tubes contain catalyst material. The collector is thermally insulated. The exhaust gas from the burners inside the combustion chambers is directed through the so-called cathedral for heat recycling by heat exchange in the convection section. Both exhaust and process gas will flow in an upward direction inside the combustion chamber and the reformer tubes respectively. This will extend the life expectancy of the catalyst and improve the performance of the catalyst because of reduced strain to the catalyst at the warmest zone. Furthermore, exhaust gas fans with less capacity may be used and a better flame distribution is achieved due to the natural convection inside the combustion chamber. The use of a transfer line is avoided when used inside the plant according to the invention, resulting in less maintenance and insulation in form of insulation tiles and cemented material, less repair to the pressurised casing, lower risk of shut-down due to poor insulation or the condition of the pressurised casing, which also provides a safer operation. Furthermore, lower investment, less heat loss and less loss of pressure is achievable The reformer according to the invention combines burners installed at the bottom with the streaming direction being turned around, which is not previously known.