Patent Application
20130048916
This invention relates to a method and a device for carbon injection and recirculation of gases when producing synthesis gas from solid carbon particles, wherein the carbon particles are preferably obtained by pyrolysis and gasification of the carbon particles is effected by heating the carbon particles indirectly in the presence of a process gas in the same space in which the carbon particles are situated, the reaction product being recirculated and the synthesis gas produced during the gasification being discharged from the said space. In order to achieve the best possible effect, the device includes a Laval nozzle for accelerating gases to supersonic speed and for creating negative pressure for the injection of powdered carbon and longer dwell times for gas and powdered carbon in the gasification reactor.
Devices for carbon injection when producing synthesis gas are required to allow for the gasification of carbon-bearing material in a gasification process.
Gasification is a process for producing gaseous fuel from solid fuel. The technique is used for coal, residual products of coal, petroleum residues, waste and biomass. The reactions are based on oxidising gases (e.g. CO2 and H2O) being heated by substoichiometric combustion and then reacting with carbon ([C] reducing agent), with carbon monoxide (CO) and hydrogen (H2) being formed as heat is consumed in order to carry on the reactions, which are endothermic. The gaseous mixture of carbon monoxide (CO) and hydrogen (H2) is usually referred to as synthesis gas.
One common gasification method is the highly substoichiometric combustion of carbon-bearing materials while supplying superheated steam. The combustion supplies the system with heat and flue gases (CO2 and H2O). Carbon which is not burnt but is now superheated reacts with flue gases and the steam supplied. The carbon (C) reduces carbon dioxide (CO2) to carbon monoxide (CO) and water vapour (H2O) to hydrogen (H2). The heat consumed lowers the temperature and reactivity decreases. Carbon reactivity is highly temperature-dependent, while the equilibrium of the reactions is temperature-dependent. Oxygen-based combustion is currently the predominant combustion method in connection with gasification, although air-based combustion is also found. Most processes are based on a pressurised system. Steam and oxygen are easily pressurised and rarely cause problems. The introduction of, e.g. pulverulent material into the reactor means that a pressure difference between the atmosphere outside the gasification reactor and the pressure inside it has to be overcome.
The problem with the gasification of carbon-bearing materials such as coal, residual products of coal, petroleum residues, waste and biomass as described hereinabove consists in maintaining a sufficiently high temperature for a sufficiently long period of time to achieve the complete gasification of carbon-bearing material, effecting sufficient mixing of oxidising gases (CO2 and H2O) with the reducing agent (carbon) and overcoming pressure differences between the atmosphere outside and inside the gasification reactor. If the time and temperature cannot be maintained, the reaction will not be carried on to its completion, with insufficient mixing also leading to an incomplete reaction.
This invention is a device for carbon injection when producing synthesis gas which injects pulverulent material by means of a tubular injector, wherein the solid material goes into the centre thereof and a surrounding nozzle device of the Laval type for oxidising gases for creating a strong negative pressure which sucks the carbon into the injector and furthermore distributes it into the gasification reactor effects the increase in pressure, extends the dwell time in the reactor and creates a homogeneous mixture therein. The strong momentum of the oxidising gases brings about vigorous mixing of the synthesis gas in the gasification reactor with the incoming oxidising gases and the pulverulent material. The negative pressure created by the gas momentum can be controlled by recirculating some of the synthesis gas in the gasification reactor through the injector in channels provided to this end therein.
A first aim of this invention is to provide a device of the type defined in the introductory part, an essential principle of this invention being to create a negative pressure in order to facilitate the introduction of pulverulent material into the gasification reactor by means of the injector.
Another aim of this invention is to create vigorous agitation between the oxidising gases and the pulverulent material as they are introduced into the gasification reactor and to recirculate synthesis gas in the gasification reactor, thereby achieving uniformity of temperature and composition. This results in a longer dwell time in the reactor and thus allows for a more compact reactor design.
Yet another aim of this invention is to recirculate synthesis gas through the injector and to control the negative pressure as pulverulent material is introduced into the gasification reactor in this manner.
At least the first aim of this invention is achieved by means of a device having the features specified in independent claim 1 hereinafter. Preferred embodiments of the invention are defined in the dependent claims.
One preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which:
The region in which the central tube 6 of the injection nozzle 1 opens into the gasification reactor 2 defines an inlet area for the powdered carbon C. The negative pressure in the centre of the injection nozzle 1/inlet area sucks out powdered carbon C and recirculated reaction product Rs where the three streams are mixed and the gasification reaction starts. The process gas P flowing at supersonic speed through the annular Laval nozzle 15 also results in further recirculation from the periphery thereof. Further reaction product is incorporated into the gasification mixture from the injection nozzle 1 in the centre of the mixing zone M immediately in front of the injection nozzle 1 itself. Heat from the recirculated reaction product Rs helps the indirect radiant heat in the gasification reactor 2 to rapidly increase the temperature of the injected powdered carbon C and process gas P to reaction temperature for the gasification process.
The pipes, tubes, etc. connecting the units of the plant are not described nor shown in detail. The pipes, tubes, etc. are designed in a suitable manner to perform their function, i.e. to transport gases and solid substances between the units of the plant.
Solid carbon particles C are supplied to the injection nozzle 1 together with the process gas P and some of the recirculated secondary reaction product Rs. The negative pressure for the carbon injection can be controlled occasionally as a result of the fact that the secondary reaction product Rs flows through separate channels 14 in the injection nozzle 1. The carbon particles C preferably originate from pyrolysis preceding the gasification. The size of the carbon particles C is preferably adapted to give the fastest possible reaction in the reactor. The process gas P can be steam or recovered and purified flue gas from, e.g. the combustion phase heating the reactor. If the process gas P is recovered flue gas, it can contain both water vapour (H2O) and carbon dioxide (CO2). The process gas P is normally preheated by heat recovered from the outgoing synthesis gas S in a downstream heat exchanger. The process gas P normally has an excess pressure which is sufficiently high relative to the reactor pressure to achieve supersonic speed. The process gas P having a speed Mach>1 creates strong momentum in the gasification reactor 2. The pressure for steam is dependent on the temperature out of the abovementioned heat exchanger. If flue gas is used instead of steam, the pressure of the recirculated flue gas is normally created by a compressor. The momentum of the process gas P out of the injection nozzle 1 results in the recirculation of secondary reaction product Rs entrained into the reaction zone R in the mixing zone M. The reaction taking place in the gasification reactor 2 is that the carbon C reduces the contents of the process gas P (H2O and CO2) to synthesis gas S (H2 and CO), this reduction consuming the heat supplied to the process by burners 4 which heat indirectly. Heat is supplied to the gasification reaction by radiation from burners 4, with the combustion taking place inside radiant tubes in that fuel F and oxidising agent O are burnt to give flue gas FG, i.e. separated from the gasification flow. There is no direct gas yield in the gasification reactor 2 between burners 4 and process gas P or its reaction products. By imparting supersonic speed to the process gas P, the injection nozzle 1 provides for an extended dwell time in the reactor 2 and the gasification reaction can be carried on closer to equilibrium. This also results in the greatest possible degree of burn-out for the carbon particles C.
Outgoing synthesis gas S can be used as energy gas for combustion purposes or as the basis for further refinement to liquid fuels (Fischer-Tropsch process for typical vehicle fuels, methanol production or the like).
The injection nozzle 1 is designed to handle different system pressures in the gasification reactor 2. The pressure in 2 can be controlled from atmospheric pressure to very high pressure (>100 bar). The injection nozzle 1 is typically designed with a ceramic part adapted to the ceramic lining in the gasification reactor 2 and an outer part made of heat-resistant steel, in which channels for carbon (C), process gas (P) and recirculated reaction gas (Rs) are located and are ultimately brought together out of the lower end of the nozzle. The injection nozzle must always have a feed pressure for the process gas P higher than the system pressure in the gasification reactor 2. This pressure difference also creates the negative pressure which sucks out carbon particles C and entrains secondary reaction product Rs. The Laval nozzle 15 creates a strong negative pressure in relation to the mass flow of process gas P as the pressure is high compared to a standard injector with straight tubes. The strong negative pressure from the Laval nozzle 15 is advantageous for controlling the ratio between the mass flow of carbon C and the process gas P in the gasification reactor 2 and thereby for achieving optimum reaction conditions.
The choice of material for the injection nozzle 1 depends on the temperature in the gasification reactor 2, which in turn depends on the reaction temperature, to achieve the maximum yield of synthesis gas S. A typical value is in the range of 900-1300° C. The choice of material for ceramic and metal parts in the injection nozzle 1 is adapted to the selected temperature level. Temperature uniformity in the reaction zone R is achieved more rapidly than in the case of normal injection nozzles as a result of the recirculation of reaction gas Rs partly through the channels 3 in the injection nozzle 1 and partly through the mixing zone M.
The synthesis gas S (H2 and CO) from the gasification reactor 2 contains hydrogen and carbon monoxide, as well as a certain amount of carbon dioxide and methane depending on the composition of the incoming process gas P and the selected temperature.
In an alternative embodiment, the injection nozzle can be used with a mixture of process gas as described hereinabove with the addition of oxygen, this significantly increasing the temperature in the mixing zone M and the reaction zone R.
In another alternative embodiment, the injection nozzle is horizontal, the carbon injection C then taking place in the horizontal plane or as close to the horizontal plane as the process will allow.
Feeding of the powdered carbon C can be effected by means of a hydraulic piston instead of a feed screw as described in
When a gastight carbon feed system subjected to negative pressure is used, the pressure-regulating channels 14 in
In the embodiment described hereinabove, a secondary reaction product Rs is recirculated via channels 14 arranged in the injection nozzle 1. As an alternative to this arrangement, the synthesis gas S discharged from the gasification reactor 2 can instead be recirculated in the central tube/central channel 6 of the injection nozzle 1. From a purely practical point of view, this is achieved by means of a recirculation pipe arranged external of the gasification reactor 2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1000461-2 | May 2010 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE11/00079 | 5/5/2011 | WO | 00 | 11/1/2012 |
