Integrated method for gasification and indirect combustion of solid hydrocarbon feedstocks in a chemical loop

Abstract

The invention relates to an integrated method for gasification and indirect combustion of a solid hydrocarbon feedstock in a chemical loop, comprising: contacting solid hydrocarbon feedstock (1) with water (2) in a gasification reaction zone RG in order to discharge ashes (9) and to produce a gaseous effluent (3) comprising syngas and water, supplying reduction reaction zone RR of a redox chemical loop with at least part of gaseous effluent (3) produced in the gasification reaction zone in order to produce a CO.sub.2 and H.sub.2O-concentrated gaseous effluent (4), reoxidizing the oxygen-carrying solid particles from reduction reaction zone RR of the chemical loop in oxidation reaction zone RO by means of an oxidizing gas (6) and discharging fumes (7). The invention also relates to a plant allowing said integrated method to be implemented.

Claims

1. An integrated method for gasification and indirect combustion of a solid hydrocarbon feedstock in a chemical loop, comprising: contacting solid hydrocarbon feedstock with water in a gasification reaction zone RG to conduct an endothermic gasification reaction, discharge ashes and produce a gaseous effluent comprising syngas CO, H.sub.2 and H.sub.2O, wherein oxygen for the endothermic gasification reaction is supplied only from the water or the water and CO.sub.2; supplying reduction reaction zone RR of a redox chemical loop wherein oxygen-carrying solid particles Me/MeO circulate with at least part of gaseous effluent comprising syngas CO, H.sub.2 and H.sub.2O produced in the gasification reaction zone to reduce the oxygen-carrying solid particles Me/MeO and combust the syngas to produce a CO.sub.2 and H.sub.2O-concentrated gaseous effluent; and reoxidizing the oxygen-carrying solid particles from reduction reaction zone RR of the chemical loop in oxidation reaction zone RO by means of an oxidizing gas and discharging fumes; wherein contacting of the solid feedstock with water in the gasification reaction zone is performed without direct contact with the oxygen-carrying solid particles Me/MeO, and wherein energy required for the endothermic gasification reaction in gasification reaction zone RG is provided at least partly by exothermic combustion of all or part of the syngas in the redox chemical loop.

2. An integrated gasification and chemical looping combustion method as claimed in claim 1, wherein a part of the CO2 and H.sub.2O-concentrated effluent produced in reduction zone RR is recycled so as to supply gasification reaction zone RG with oxygen.

3. An integrated gasification and chemical looping combustion method as claimed in claim 1, wherein reduction reaction zone RR is supplied with all of the gaseous effluent produced in gasification reaction zone RG in order to produce heat that is recovered in oxidation reaction zone RO or on the gaseous effluent transport lines.

4. An integrated gasification and chemical looping combustion method as claimed in claim 1, wherein reduction reaction zone RR is supplied with only a part of the gaseous effluent produced in gasification reaction zone RG in sufficient amount to produce the energy required for the gasification reaction, a remainder of the gaseous effluent produced in gasification reaction zone RG not supplied to the reduction reaction zone RR allowing syngas CO+H2 to be produced.

5. An integrated gasification and chemical looping combustion method as claimed in claim 1, wherein the solid hydrocarbon feedstock is selected from among coal, coked catalysts from the fluidized bed catalytic cracking method or cokes produced by flexicoker units.

6. An integrated gasification and chemical looping combustion method as claimed in claim 1, wherein the oxygen-carrying solid particles Me/MeO in the reduced state Me are sent directly from the reduction reaction zone RR to the oxidation reaction zone RO.

7. An integrated gasification and chemical looping combustion method as claimed in claim 2, wherein the part of the CO2 and H2O-concentrated effluent is supplied to a feed point of the gasification reaction zone RG comprising water in liquid form, and wherein the method further comprises cooling the fumes from the oxidation reaction zone RO in at least one heat exchanger by heat exchange with the water in liquid form, thereby heating the water in liquid form to provide water in vapour form and/or under pressure, the water in vapour form and/or under pressure being supplied to the gasification reaction zone RG.

Description

LIST OF THE FIGURES

(1) FIG. 1 shows the integrated method according to the invention with gasification of the solid fuel, then chemical looping combustion of the syngas produced, in its application for heat production.

(2) FIG. 2 shows the integrated method according to the invention with gasification of the solid fuel, then chemical looping combustion of part of the syngas produced, so as to provide the energy required for gasification of the feedstock, in its application for syngas production.

(3) FIG. 3 illustrates the example and represents the thermodynamic equilibrium results of 90% H.sub.2O and 10% Carbon simulated with the CHEMKIN software.

DESCRIPTION OF THE FIGURES

(4) The system for implementing the integrated gasification and chemical looping combustion method according to the invention is made up of three main reactors: a gasification reactor RG, a reduction reactor RR and an oxidation reactor RO.

(5) Description of FIG. 1:

(6) FIG. 1 illustrates the method according to the invention with indirect combustion of the solid hydrocarbon feedstock for heat production.

(7) Solid fuel (1) is first gasified in the presence of water vapour (2) in gasification reactor RG. The effluent obtained (CO+H2) comprising syngas CO+H2 (3) is then carried to reduction reactor RR where the gas is burnt in contact with the oxygen carrier (Me/MeO) that circulates in the chemical loop as particles. Combustion gas (4) leaving reduction reactor RR essentially contains CO.sub.2 and H.sub.2O. Thus, the CO.sub.2 can be readily separated by condensing the water vapour. A fraction of this gaseous effluent essentially comprising CO.sub.2 and H.sub.2O (5) can be injected into gasification reactor RG in order to maintain the temperature or to supply oxygen for gasifying the fuel. The oxygen carrier in the reduced state Me is then sent to oxidation reactor RO where it is reoxidized on contact with the air introduced as oxidizing gas (6). The oxidation degree difference between the oxygen carrier in the reduced state (Me) at the outlet of RR and the oxygen carrier in the oxidized state (MeO) at the outlet of RO is X.

(8) A heat exchanger E present in oxidation reactor (E1) or on a transport line (E2) carrying the fumes from oxidation zone RO allows the energy to be recovered in form of heat.

(9) In a preferred embodiment, the fumes from oxidation zone RO (7) can be cooled in exchanger E2 by heat exchange with water in liquid form (8) in order to supply the gasification reactor with water (2) in vapour form and/or under pressure. This also affords the advantage of discharging cooled fumes (7) from the plant. Ashes (9) are also discharged of the plant from gasification zone RG.

(10) Description of FIG. 2:

(11) FIG. 2 illustrates the integrated method according to the invention with gasification of the solid hydrocarbon feedstock allowing both production of syngas CO+H2 and production of the heat required for the gasification reaction. The scheme of the gasification and indirect combustion system in its application for the production of syngas is presented in FIG. 2. This system is similar to the configuration of the combustion method presented above, with a modification at the outlet of gasification reactor RG for gas (3). In this scheme, only a fraction of syngas (3a) produced in RG is sent to combustion reactor RR to produce the heat required for gasification. The other part of the syngas (3b) is considered as the product of the process and it is discharged from the plant. The water vapour in the syngas can be condensed later so as to improve the calorific value of the gas.

(12) The method can thus be used to produce syngas. This syngas can be used as feedstock for other chemical conversion methods, for example the Fischer-Tropsch method allowing to produce, from syngas, liquid hydrocarbons with long hydrocarbon chains usable as fuel bases.

Advantages of the Method According to the Invention

(13) The method according to the invention has many advantages.

(14) Since there is no direct contact between the oxygen carrier and the (previously gasified) fuel, the device allowing to implement the method according to the invention can be readily adapted to existing combustion methods by replacing the inflowing air by water vapour and CO.sub.2.

(15) The integrated method according to the invention makes a solid-solid separation (oxygen carrier-unburnt solid fuel) unnecessary since the fuel is only contacted with the oxygen-carrying particles once gasified, a separation that was necessary so far in the published CLC methods for solid feedstocks.

(16) The method according to the invention, in its two embodiments, can operate at a high pressure in gasification reactor RG, whereas reactors RO and RR operate at atmospheric pressure. This notably allows to produce syngas at high pressure (for the Fischer-Tropsch method for example). Furthermore, since reaction zones RO and RR operate at atmospheric pressure, the integrated method according to the invention allows to decrease the operating cost and the cost of the building materials for reactors RO and RR. Finally, fuel leakage to reactors RO and RR is minimized, as well as the loss of oxygen carrier to gasification reactor RG.

(17) Gasification being carried out with water vapour and not with air (absence of nitrogen), the syngas obtained has a high calorific value.

(18) Gasification being carried out with water vapour and not with air (absence of nitrogen), the production of nitrogen oxides is minimized.

(19) The main limit of these methods is the supply of heat to the gasification reactor because the gases have a limited heat capacity. In a preferred embodiment, overheated water vapour is injected (at a temperature advantageously close to 1000 C. for example). It can be noted that, by means of water vapour injection (and possibly CO.sub.2 from the fumes coming from the reduction zone), 2 to 5 times as much oxygen is supplied to the gasification reactor in relation to the case where only air is injected directly into the reactor. This difference is due to the fact that the nitrogen in the air is replaced by H.sub.2O or CO.sub.2.

(20) Gasification can be carried out at atmospheric pressure or under pressure. In case of gasification under pressure (for example at pressures ranging between 5 and 50 bars, preferably between 20 and 40 bars), the water vapour required for gasification results from a vapour cycle supplied at least partly with water resulting from the fumes of the reduction reactor wherein the heat required for preheating and pressurizing the vapour is recovered by exchange with the fumes of oxidation reactor (RO).

(21) Various types of reactor can be used in the different reaction zones RG, RO and RR of the method according to the invention. Gasification reactor RG can notably be a circulating fluidized bed or an ebullating fluidized bed boiler. The technological range of oxidation RO and combustion RR reactors that can be selected is also wide. These reactors can be ebullating fluidized bed or circulating bed reactors.

(22) The solid hydrocarbon feedstocks used in the method according to the invention can be selected from among all the types of solid hydrocarbon fuels, notably coal, biomass, coked catalysts from the fluidized catalytic cracking process (FCC) or cokes produced by the flexicoker process, taken alone or in admixture.

(23) The hydrocarbon feedstocks are fed into gasification reactor RG in form of a dispersed solid of average diameter generally ranging between 10 microns and 5 mm, preferably between 50 microns and about 1 mm.

(24) The efficiency of the chemical looping combustion (CLC) method using a circulating fluidized bed is due to a large extent to the physico-chemical properties of the redox active mass. The reactivity of the redox pair(s) involved and the associated oxygen transfer capacity are parameters that influence the dimensioning of reactors RO and RR, as well as the rates of circulation of the particles. The life of the particles depends on the mechanical strength of the particles and on the chemical stability thereof. In order to obtain particles usable for this method, the particles used generally consist of a redox pair or of a set of redox pairs selected from among CuO/Cu, Cu2O/Cu, NiO/Ni, Fe2O3/Fe3O4, FeO/Fe, Fe3O4/FeO, MnO2/Mn2O3, Mn2O3/Mn3O4, Mn3O4/MnO, MnO/Mn, Co3O4/CoO, CoO/Co, and of a binder providing the required physico-chemical stability. Synthetic or natural ores can be used.

(25) Big particles are more difficult to transport and require high transport rates. In order to limit the transport rates in the transfer lines and within the reactors, and thus to limit pressure drops in the process, as well as abrasion and erosion phenomena, the size of the oxygen-carrying material particles is therefore preferably limited to a maximum value close to 500 microns.

(26) Preferably, the grain size of the oxygen-carrying material fed into the chemical looping combustion plant is such that more than 90% of the particles have a size ranging between 100 and 500 microns.

(27) More preferably, the grain size of the oxygen-carrying material fed into the plant is such that more than 90% of the particles have a particle diameter ranging between 150 and 300 microns.

(28) More preferably yet, the grain size of the material fed into the plant is such that more than 95% of the particles have a diameter ranging between 150 and 300 microns.

(29) The method according to the invention can be advantageously integrated in a refinery.

EXAMPLE

(30) In the example below, the main reactor is the gasification reactor (RG). FIG. 3 shows the thermodynamic equilibrium concentrations (Xeq) of the gases in reactor RG. These results clearly show that, at equilibrium, nearly all of the carbon injected is converted to CO.sub.2. The CO concentration is very low at approximately 600 C., but it increases with the temperature. This graph and the material balance are used to calculate the various gas proportions at the outlet of reactor RG.

(31) The thermodynamic equilibrium results of 90% H.sub.2O and 10% carbon were therefore simulated with the CHEMKIN software.

(32) A steady state zero-order model was developed to study the feasibility of this system. The coal is injected into the bed at a flow rate of 3 kg/h. The properties of the coal injected are given in Table 1. Gasification was carried out with water vapour overheated to 1000 C. and a mass flow rate of 27 kg/s (equivalent to the stoichiometric air flow rate required for complete combustion). The properties of the syngas at the outlet of reactor RG are given in Table 2. The concentrations are calculated on the thermodynamic basis and with the material balance. The temperature at the outlet of reactor RG is 600 C. and the average temperature of reactor RG is 800 C.

(33) TABLE-US-00001 TABLE 1 Properties (ultimate analysis) of the coal used for the case studied, with LHV = 28 MJ/kg. Wt. % Components Wt. % (minus water, ashes) Carbon (C) 64% 72% Hydrogen (H) 5% 6% Nitrogen (N) 1% 1% Total sulfur (S) 1% 1% Oxygen (O) 18% 20% Ashes 12%

(34) TABLE-US-00002 TABLE 2 Concentrations of the various gases at the outlet of gasification reactor RG. Flow Flow Concentration rate rate Concentration (minus Components Wt. % (kg/s) (mol/s) (mol %) water, mol %) CO.sub.2 13.0% 3.95 0.141 8% 28% H.sub.2O 81.4% 22.93 1.273 71% CO 1.8% 0.51 0.018 1% 4% H.sub.2 2.5% 0.70 0.347 19% 68% CH.sub.4 0.0% 0.00 0.000 0% 0% N.sub.2 0.1% 0.03 0.001 0% 0% SO.sub.2 0.2% 0.04 0.0007 0% 0%

(35) All or part of the syngas produced in gasification reactor RG can be sent to the combustion reactor in order to produce energy.

(36) In the case of syngas production, only part of the gas required to maintain the overall energy balance is sent to combustion reactor RR. In the present example, the required minimum fraction to be sent to the combustion reactor is 53%. This system can thus deliver 47% of syngas as product.

(37) In the case of heat production, during combustion, all of the syngas is burnt in reduction reactor RR in order to produce energy.