FR2937967A1 - PROCESS FOR THE CONTINUOUS PRODUCTION OF HIGH TEMPERATURE OXYGEN - Google Patents

Abstract

The invention relates to a system for continuous production of oxygen diluted at high temperature. According to the invention, it is characterized by the circulation of solid particles of the mixed oxide type with perovskite structures between two fast fluidized bed reactors, the first of which is exothermic and the second is endothermic.

Description

PROCESS FOR THE CONTINUOUS PRODUCTION OF HIGH TEMPERATURE OXYGEN

1. State of the art Oxygen production is commonly obtained by distillation of atmospheric air. The cold necessary for the industrial liquefaction of the air is obtained by relaxation using the phenomenon of Joule-Thomson. The air is dusted, freed from its carbon dioxide and moisture, compressed to 200 bar, cooled in a heat exchanger, and then relaxed to 25 bar. A series of compressions and relaxations leads to liquefaction. This fractional distillation separates oxygen, nitrogen and noble gases. An example of this technology is described in WO 2007/068858. According to a first step in an air separation apparatus, all the air intended for distillation is compressed in a main compressor, at least a first compressed air flow is sent into the main compressor, purified and cooled in a line. of exchange at the medium-pressure column of a double column, the air flow is separated into flows enriched in nitrogen and oxygen in the medium-pressure column, a flow of liquid oxygen is withdrawn from the low-pressure column, it is pressurized to a high pressure and vaporized in the exchange line to form a first gaseous flow rich in oxygen and at high pressure, at least a portion of the compressed air is liquefied in the main compressor and sends the liquefied part to the double column and also produces a second gaseous flow rich in oxygen but at a lower pressure than the first gaseous flow rich in oxygen but at a lower pressure. When the first gas flow rich in oxygen and in a second step, the liquefaction pressure of the air is increased in setting the blades of the main compressor which sets this pressure, the production of the second gas flow rich in oxygen and the withdrawal of the first gaseous flow rich in oxygen is increased.

New regulations on carbon dioxide (CO2) emissions have led to the development of the field of fossil fuel oxy-combustion, a technology that can be applied in industrial boilers and large power plants. The fumes produced are then concentrated in CO2 without dilution by nitrogen, which reduces the capture of CO2 to condensation and purification against trace elements and conditioning before transport and underground storage. But the major disadvantage of the production of oxygen by distillation for use on a large scale is the significant consumption of electrical auxiliaries to drive the various compressors. Thus, typical consumptions of 250 KWh per ton of oxygen are necessary, although dependent on the level of purity sought in the oxygen produced. Another major disadvantage is the very high consumption of cooling water, necessary to evacuate the losses of these compressors. This is a real blocking point in locating future plants and converting them to oxy-fuel combustion. These drawbacks result in a loss of efficiency of the plants of about 10 points, which cancels out the developments of the fossil fuel solid power plants made for 40 years, and leads to a very significant increase in the production costs of the plants. electricity.

The feasibility of adapting oxy-combustion to the global fleet of boilers is directly related to the lock that is massive production of oxygen at minimum cost. There is an industrial alternative to distillation that relies on the use of polymer membranes but is reserved for small capacity production. There are also systems called PSA and TSA (pressure and temperature swing adsorption) but they are also suitable for small installations. Another problem is the capacity of these units of more than 15,000 tons per day of oxygen for 1000 MWe plants while the commercial size of the distillation units is about 4000 tons of oxygen per day.

Finally, there is a new oxygen production technology using ceramics called perovskites having a particular structure and properties known since 1860. Perovskite is a crystalline structure common to many oxides. This name first designated calcium titanate CaTiO3 formula, before being extended to all oxides of general formula ABO3 having the same structure. Perovskites are of great interest because of the great variety of properties according to the choice of elements A and B. An example of these properties is described in the following article: Mixed conduction and oxygen permeation in the oxides for CaTiO3, IWAHARA H. (1); ESAKA T.; MANGAHARA T.; (1) Tottori University, College. eng., dep. Environmental Chemistry Technology, Tottori 680, JAPAN Journal of Applied Electrochemistry 1988, vol. 18, no. 2, pp. 173-177. On this basis, the so-called ceramic autothermal recovery (BOC Company) has been developed which uses these oxygen storage properties of high temperature perovskites to adsorb oxygen from the air in a fixed bed of particles and then to release it by sweeping. of gas for example recycled fumes or steam. The process operates in a similarly continuous way by combining the operation of two fixed beds in cyclic mode. The air and the purge are carried out against the current to reach a high purity of oxygen and recover the heat of the two gaseous currents leaving the bed. Indeed the adsorption of oxygen by the perovskites is exothermic while the release of oxygen is endothermic, knowing that the process must globally operate autothermically with negroins an external thermal contribution. To smooth the production of oxygen with respect to use, knowing that the process is continuous, a dilute low pressure oxygen storage tank is necessary. This is a real disadvantage of investment and exploitation. But the latter method relies on the use of fixed beds operated in cyclic mode, which makes it unsuitable to meet the oxygen needs of 15,000 tons / day of large fossil fuel solid power plants. Unless you multiply the fixed beds by tens, which is not economical.

2. Problem posed It is a question of proposing a completely continuous system of production of diluted oxygen at high temperature, which can be extrapolated to very large production capacities (15 000 to 20 000 tons / day), minimizing the consumption of auxiliaries , also minimizing the consumption of cooling water and able to follow the load variations of the boilers that the system supplies with oxidizer. The process must operate globally in autothermicity. The ability to perform this production by a single unit and not multiple trains leads to very significant reductions in capital cost. 3. OBJECT OF THE INVENTION The invention proposes to use a new architecture of two interconnected high-flux fast fluidized bed solid-acid reactors with very high flux of circulating solids, which alone, thanks to this high and continuous circulation, can solids of the type mixed oxides. perovskites structures, to transfer the necessary oxygen selectively and to carry out on the circulating solids the heat exchanges created by the exothermicity and the endothermicity of the reactions with the oxygen, and no longer to carry out these exchanges. heat on gas currents against the current. This type of reactor is perfectly adapted to the high temperature (750 to 1150 ° C) in order to accelerate the kinetics of exchange and it makes it possible to reach the total autothermicity thanks to specific formulations of oxides and thanks to the fact of circulating tens of thousands of tons per hour of solids, the throughput required by large applications.

4. Description of the Invention See Figures 1, 2 and 3 The invention comprises a first fast fluidized bed reactor (1) whose inventory consists of solid particles of the mixed oxide type with perovskite structures, operating at high temperature and fluidized by air (2). The exothermicity of the adsorption / oxygen absorption reaction in this first reactor is controlled by an exchanger (3) on the circulating solids (4) whose adjustable flow rate makes it possible to precisely adjust the optimal adsorption temperature in the loop. On this loop (4) is withdrawn a flow of solid particles (5) of the mixed oxide type structures of perovskites, high temperature particles having absorbed oxygen from the air to a second reactor (8) fluidized fast fluidized bed by CO2 (7) mixed with water vapor, in which will release the oxygen. This reactor (6) is endothermic and uses the heat of the solids from the first reactor to effect this release. The solids flow taken from the first reactor (1) must therefore meet this need for heat. Then the solids freed of their oxygen (8) are transferred to the first reactor (1) for a new cycle. One of the difficulties is to control the degree of oxygenation and deoxygenation in the transferred solids. This is solved by taking the solids on each loop (9 and 10) at the level not of the actual reactors (1 and 6) but at the level of the outer loop in fact at the bottom (11 and 12) of the return duct. so that the solids remained long enough in each reaction zone in terms of temperature, residence time. The perovskites used must have sufficient mechanical strength for resistance to abrasion and erosion created by fluidization and shocks, as well as having a particle size adapted to rapid fluidized beds and their interconnection. Given the wide range of possible composition of perovskites, it appears that the mixed oxides of structure Calcium Iron Titanium, Calcium Cobalt Titanium, Calcium Nickel Titanium are adapted to this transfer of oxygen at high temperature. The addition of copper and / or manganese mixed or substituted with iron and nickel is also proposed in view of their oxidation properties. The system includes a system for introducing fresh solids (15) and used solids (13 and 14).

The gas streams (16 and 17) from each reactor (1 and 6) are partially cooled in exchangers (18 and 19), for example of the steam type. The gaseous stream containing the oxygen-depleted air (17) is released to the atmosphere after cooling to 90 ° C and filtering (20) while the stream (16) of oxygen and CO 2 and H 2 O 2 scanning gas is transferred at high temperature by a special jacketed sheath (18) to the boiler to be operated in oxy-combustion. The outer annular space of the double jacket of this sheath under light pressure contains CO2 and H2O from the boiler operating in oxy-combustion (19). Part of this stream O2 / CO2 / H2O can be recycled (7) to the first reactor (1) by mixing with the air (2) fluidization to drive the autothermicity of the assembly and the operating temperature levels of each reactor (1 and 6). This can result in a slight loss of CO2 to the atmosphere by the outlet of the first reactor but provides an ultimate set temperature adjustment. 5. Essential elements The system for the continuous production of high temperature diluted oxygen according to the invention is specific for: the circulation of solid particles of the mixed oxide type with perovskite structures between two fast fluidized bed reactors, the first of which is exothermic and the second is endothermic

The two fast fluidized bed reactors are interconnected by the lower part of their external solids circulation loop

• the temperature control of the second endothermic reactor is ensured by the supply of solids from the exothermic reactor • the temperature control of the first exothermic reactor is ensured by the adjustable cooling of the solids taken from the outer loop or in an exchanger integrated in the reactor fast fluidized bed.

• the fluidization of the first fast fluidized bed reactor is provided by air • the fluidization of the second fast fluidized bed reactor is provided by a mixture of CO2 and H2O under slight pressure from a boiler operating in oxy-combustion 15 • the discharge to the atmosphere of the oxygen depleted air at high temperature from the first reactor after cooling and filtration • the high temperature transfer of the O2 / CO2 / H2O mixture from the second fast fluidized bed reactor to a working boiler In combustion oxy-20 • a concentric double-shelled transfer sheath externally containing the cold fluid at a slight pressure of CO2 H2 and internally the hot fluid O2 / CO2 / H2O. Solid particles of the mixed oxide type with perovskite structures with a particle size mainly comprised between 10 and 100; solid particles of the mixed oxide type with perovskite structures of Calcium Iron Titanium, Calcium Cobalt Titanium and Calcium Nickel composition with addition of copper and / or manganese • a high temperature operation (750 to 1150 ° C) of the two fast fluidized bed reactors.