ES2547465A1 - Calcination procedure with pure co2 production mediantecombustion using o2 transporters (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Calcination procedure with production of pure2 co by combustión using o2 carriers. The objective of the described procedure is to produce a stream of calcined solids rich in cao and a pure or almost pure stream of co2 from a solid stream rich in caco3, by a stream of solids heated to very high temperature by a process of oxidation of said solids with air. The current rich in cao can be used as feed for clinker kilns in cement plants or for co2 capture processes. (Machine-translation by Google Translate, not legally binding)

Description

SECTOR OF THE INVENTION

Calcination processes. Process for the production of cement. CO capture processes ,. 10 STATE OF THE TECHNIQUE

Numerous international organizations and governments consider the capture and geological storage of COz generated in large stationary sources as a tool for reducing greenhouse gas emissions into the atmosphere. Cement production is responsible for more than 5% of the total emissions of COz into the atmosphere. Cement plants are sources of CO2 emission in which CO2 capture and storage technologies can be applied_ For cement, the most studied technologies are flue gas scrubbing, scrubbing, or

20 combustion of the fuel with highly concentrated Oz ("oxy-combustion"), previously obtained by air separation. These systems are expensive, and minimizing the cost of capturing COz is key for capture technologies to reach a commercial scale in the cement sector.

The patent applied for as JPS5767013 (published as JP19800138661) describes a process for obtaining high purity COz from calcining CaC03 with CaO previously reheated to very high temperature (950-120QoC) in a bubbling fluidized bed combustor. In this process, part of the calcined solids (mainly CaO) act as heat carriers from the combustion chamber to the

30 calciner The use of bubbling beds makes the processing capacity per unit area of this system very modest. There are also great limitations to the circulation of solids in the chosen system of interconnected beds, which makes the system proposed in the JPS5767013 patent not the most suitable for the capture and large-scale storage of the COz generated by calcination in large sources

35 stationary COZs such as cement plants or other large industrial calcination systems. A possible solution to overcome the above limitations is to use

Fluidized bed combustors circulating and taking advantage of its high heat transfer capacity thanks to its large capacity of circulation of solids between reactors. There are proposals to achieve this objective in practice, as described in the publication of Rodríguez et al. Process for capturing CO2 arising from the calcination of the CaD used 5 in cement manufacture, Environ. ScL Technol. 2008, 42, 6980--6984, or in patent application W02012 / 152899A. It is also evident from the state of the art (Romano et al., Application of the Sorption Enhanced-Steam Reforming process in combined cycle-based power plants, Energy Procedia, 2011, 4, 1125-1132) that any of the above processes will be seen benefited by a preheating of the carbonate stream entering the calciner, by contacting said carbonate flow with the hot CO2 rich gas leaving the calciner. This last preheating stage allows preheating

the CaC03 above 800 ° C without decomposing it.

Despite the theoretical advantages of the calcination process of CaC03 with a recycle of CaD

15 reheated, all the processes described in the previous paragraph have a very important limitation in terms of their overall CO2 capture efficiency (which does not exceed 5060% of the total carbon entering the system as CaCOJ and as fuel). This is because the pure CO2 that is obtained in the calciner is only that which comes from the

decomposition of the CaCOJ in said calciner. The CO2 generated in combustion with air

20 of the fuel necessary to heat the CaD acting as a heat carrier, is emitted into the atmosphere as a combustion gas, or requires an additional expensive system for the capture of said CO2 by any of the methods of the state of the art.

Also relevant for the purpose of this invention are a family of procedures for

25 combustion described in the state of the art (US5509362, US5827496) and which basically consist of avoiding direct combustion with fuel air. This is achieved by transporting the oxygen necessary for combustion by an oxidized solid, making use of reversible oxidation reactions with high temperature air of a metal or metal oxide to give a metal oxide with a higher degree of oxidation that is capable of

30 also be reduced at high temperature with a fuel that oxidizes, mainly CO2 and H20. These processes of combustion ("chemical looping combustion") of a fuel by means of a solid oxygen carrier (for example oxides of Fe, Ni, Ti, Cu, Mn, etc.) are in development for a great variety of processes destined to the electricity or hydrogen generation from natural gas, coal or biomass (Adanez et al, Progress

35 in chemical looping combustion and reforming technologies, Progress in Energy and Combustion Science, 2013, 38, 215-282), taking advantage of the very high reactivity of some of these materials both in the oxidation and reduction stages and their great stability

thermal and mechanical, even during processing in fluidized bed reactors operating at high speeds.

The present invention proposes a new CO2 capture method to solve the problem of efficient calcination of a continuous flow of CaCOJ, generating a stream of CaD and a separate stream of gas highly concentrated in CO2.

DESCRIPTION OF THE INVENTION

The objective of the process described in this invention is to produce a stream of calcined solids rich in CaD and a pure or almost pure stream of CO2 from a solid stream rich in CaCOJ, previously preheated to a temperature close to the equilibrium temperature of calcination.

15 The process of calcining the preheated stream of CaCOJ is carried out by continuously mixing it with a stream of dense solids superheated at temperatures higher than those of calcination. The method is characterized in that it comprises at least the following cyclic stages:

I) a first stage of generating a stream of dense solids superheated at very high temperature by the oxidation reaction in air of said solids. ii) a second stage at a lower temperature where successively the

25 calcination of the fed CaC03, the reduction with a fuel of the oxidized dense solids that come from the first stage, the separation by segregation of the partially reduced dense solids and the CaD generated in the calcination, and the extraction of the streams separately CaD product and partially reduced dense solids that are fed to the first stage.

30 iii) use of the CaD current generated in the previous stage

In a preferred configuration, the first stage is carried out in a circulating fluidized bed, fed with a flow of air (preheated by some of the high temperature material streams that are generated in the process object of this invention) capable of oxidizing circulating solids and overheating said solids to temperatures close to their adiabatic temperature of oxidation in air. The current of

Exhaust gases (mainly N2) from the circulating bed reactor is separated from solids

oxidized superheated by a cyclone, and the solids are directed to the second stage of the procedure.

5 In another preferred configuration of the process, the second stage is carried out in a circulating or bubbling hoisted fluid bed, fed by:

the stream of oxidized and overheated dense solids from the first stage

10 a stream of preheated CaC03 at a temperature close to that of its calcination in a CO2-rich atmosphere, a fuel that is fed from the bottom and that is able to reduce the dense and oxidized solid in the first stage and generate mainly CO2 and H20 as a product of said solid reduction and gas oxidation.

Optionally, a certain steam flow can also be fed to this stage to facilitate the calcination of CaC03 at lower partial COz pressures due to the steam dilution effect.

The second stage must operate under conditions of fluidization such that they allow a certain segregation of the particles of the dense solid that acts as a heat and oxygen transporter from the first stage to the second stage of the process. Thus, these separate currents leave the second stage:

A stream of gases rich in CO2 and steam constituting the gaseous product of the calcination process of CaC03 a stream rich in reduced dense solids, which is recycled to the reactor of the first stage a stream rich in CaO that constitutes the solid product of the Procedure of

30 calcination

In another configuration of the process, the solid that oxidizes in the first stage and is reduced in the second is a material with a variable iron content, preferably Fe30. which oxidizes to Fe20 3. Other materials containing various proportions of metals

35 such as Ni, Mn, Ti, etc., can also be used in specific applications. However, an advantage of iron materials is its low cost and its acceptability as 5

minor component in the production of clinker, to which the stream rich in CaD can be seen. This facilitates the practical separation of solids by segregation in the second stage, since higher iron oxide content in the stream rich in CaD will be acceptable.

In addition, favorable properties of iron oxides in combustion systems with oxygen transporters, especially suitable for the operating conditions of the process object of this invention, are known in the state of the art. Furthermore, as will be illustrated in the example of the invention, it can be shown that the

10 modest oxygen transport capabilities characteristic of iron oxides are suitable for the specific process described in this invention, when the inert part of the dense solid is used as a heat carrier from the first stage to the second stage where calcination occurs .

In another preferred configuration, the first stage operates at temperatures between 950 ° and 1200 ° C and the second stage operates at temperatures preferably between 870 ° and 950 ° C.

A variant of the process is characterized by the division of the second stage into two or more separate and serial sub-stages: a first sub-stage of calcination of

20 CaCO) in contact with the current of dense superheated solids, and a second sub-stage of reduction at a lower temperature of the dense solids by reaction with a combustible gas and subsequent segregation of said dense solids with respect to the CaD resulting from calcination.

25 Since the reduction reactions of metal oxides with common fuels (natural gas or other hydrocarbons, coal, biomass) are usually endothermic, this additional stage may slightly reduce the heat demand in the calciner. For example, if the fuel is natural gas, said reduction sub-stage is carried out at a temperature lower than that of calcination (typically between 20 and 80 ° C below the temperature of

30 calcination). In addition, the expected temperatures in the reactor where the second stage is carried out (between 870 and 950 OC) allow the use of solid fuel (coal, biomass, etc.), favored in many applications due to its low cost with respect to gas. The presence of a high concentration of CaD and Fe2D3 favors (as is known in the state of the art) the gasification of solid fuel and the cracking of tars,

35 obtaining low yields to "char" or solid non-gasified fraction of the fuel. In any case, when solid fuels are used, part of the unburned solid fraction of the fuel is burned in the reactor where stage 1 is carried out,

producing a loss of CO2 and the consequent decrease in the total efficiency of CO2 capture. But this disadvantage will be compensated in many cases by the lower cost of solid fuel.

The process described in the present invention generates a stream rich in CaO that can be used as feed to a clinker kiln of a cement plant. The integration in detail of the process of invention in a cement plant, including the steps of preheating gases and solids necessary to carry out the process of this

The invention according to the examples of the invention can be considered as part of the state of the art of the cement production industry.

Likewise, the process described in the present invention for calcining CaCOJ and producing CaO can be integrated into CO2 capture systems that make use of the 15 CaO reaction with the CO2 diluted in a gas in a carbonation reactor or carbonator.

BRIEF DESCRIPTION OF THE CONTENT OF THE FIGURES

Figure 1. Scheme of a preferred configuration of the process of the invention.

Figure 2. Scheme of a preferred configuration of the invention process where the second stage is divided into two separate sub-stages: one for the calcination of the fed CaC03 and another for the reduction with a fuel of the dense solids transporting heat and oxygen along with the segregation of CaO.

EXAMPLE OF REALIZATION OF THE INVENTION

In this example, the conceptual design of the procedure represented in Figure is performed

1. The example has been raised for the production of 3000 tons / day of cement, which means

30 21.72 kg / s of CaD (1) according to the proportions of raw materials used for the manufacture of cement that are collected in the state of the art. As the high density solid, heat and oxygen transporter (2), iron oxide has been chosen for this example whose composition in weight percent is 45% Fe304 and 55% inert material. The calculations in this example are illustrative only, and have been done by solving the

35 balances of matter and energy, assuming complete conversions of solids in the reactions that take place in the different stages.

This example illustrates the design of the preferred configuration of the invention process by first resolving the heat balance around the bubbling fluidized bed (3). In said reactor (3) the calcination of the stream of CaC03 (4) and the reduction with a mixture of methane and water vapor (5) of a stream of solids must occur

5 dense oxidized (2). Both reactions are endothermic (.D..H = 171.4 kJ / mol and 141 kJ / mol, respectively). The only heat input to the reactor must come from the sensible heat provided by the oxidized solids (2), which enter at a higher temperature than the temperature of (3). In addition, in the bubbling bed (3) the separation by segregation of these dense, partially reduced solids (6), and of the CaO generated in the calcination (1) must occur.

10 For the production of 21.72 kg / s of CaO (1) it is required to feed the bed (3) a current of 38, 78 kg / s of CaC03 (4), which enter preheated to 820 ° C. It is possible to preheat to this temperature without decomposing the carbonate using the sensitive heat of the hot gas rich in COz (7) leaving (3). Part of the state of the art is the energy integration 15 in detail of this preheating stage of CaC03, which includes one or more stages.

The thermodynamic equilibrium indicates that, in order to carry out the calcination of CaC03 at a partial pressure of 1 bar of COz, temperatures above 900 oC are necessary. However, in the specific case of this example, calcination is carried out together with the reduction of iron oxides with a combustible gas (5), which generates as a reaction product a mixture of COz and water vapor (7 ). If a certain amount of water vapor is also added to the combustible gas (5), the partial pressure of COz at the outlet of the reactor (3) can be significantly reduced and at 880 ° C a carbonate calcination can be ensured

25 fast and complete.

The iron oxides selected in this example have a low oxygen transport capacity (0.032 g transferable O2 / g solid) and a high inert ratio, which helps to increase the heat transport capacity to the reactor (3). The demand for heat to carry out the calcination of the carbonate stream (4) is 6.5 MWt. The balance of heat and matter around the adiabatic reactor (3) is closed with a current

(2) of 422.22 kg / s of iron oxide, which reaches the bed (3) at a temperature of 1073 oC.

A stream of methane mixed with water vapor in a steam / fuel molar ratio of 0.5 is used as fuel. Considering that the current of a combustible gas (5) arrives preheated to 700 oC and that the carbonate (4) does so at 820 ° C, a contribution of energy to the bubbling bed (3) of 75.7 MWt is necessary to carry carry out the calcination and simultaneous reduction of dense solids at 880 oC. This implies feeding a flow (5) of 2.48 kg / s (67 vol.% Of CH4 and 33 vol.% Of H20), which implies a consumption of 3.48 GJ per ton of CaO produced. As a reaction product, a gas stream (7) at 880 ° C of 25.89 kg / s (66 vol.% CO2 and 34 vol.% H20) is obtained. The bubbling bed (3) operates in fluidization conditions that allow the segregation of dense solid particles and the CaO formed in the calcination. In this way, the current (6) of 415.88 kg / s of partially reduced iron oxide (Fe30 4), and the current (1) of 21.72 kg / s of CaO, which can be used as feed, are separated to an oven

10 clinker from a cement plant.

To produce the current (2), a highly exothermic stage (.6.H = -474.9 kJ / mol O2) of oxidation of the current (6) is required. This takes place in a circulating hoisted fluid bed (8), where an air flow (9) of 27.23 kg / s is fed, which contains the stoichiometric amount of oxygen to carry out the complete oxidation of the flow stream. solids of iron (6) coming from the bed (3) at B80 ° C. It is considered that the air enters preheated at (8) at 700 oC, by contact with any of the product streams that come out at high temperature of the system object of this invention. Under these conditions, iron solids react quickly with air and both product gas and

20 oxidized solids are heated to 1073 ° C, due to the high exothermicity of the oxidation reaction. The output stream (10) is directed to a cyclone (11) where 20.89 kg / s of product gas (12), mainly N2, is separated from a stream (2) of 422.22 kg / s of solids from oxidized iron (Fe20 3), which are fed back to the bed (3), thus completing the cyclic process of this invention.

In order to estimate in this particular example the illustrative dimensions of the reactors (3) and (8), a gas velocity of 5 mIs in the bed (8) is also considered, which would necessitate a transverse reactor area of approximately 21 m2 Under these conditions, the circulation speed of solids would be close to 20 kg / m2, which is a reasonable value.

30 for circulating fluidized bed systems. For the bed (3) an identical area of 21 m2 would lead to surface gas velocities at the exit of 0.6 mIs If a bed density of about 2000 kg / m3 and about 3 m of expanded height is assumed, the mass of the solids in the bubbling bed would be 138,000 kg, which leads to an average residence time of the solids in the bed of approximately 300 s. Since at this stage reactions take place

35 relatively fast carbonate calcination, reduction of iron oxide with a combustible gas and segregation of solid products, this time order of 9

Residence can be considered reasonable to carry out the invention procedure in practice.

Obviously, this example shows only one of the possible ways to execute the

invention process applied to the calcination of a CaCOJ stream using

Dense solids heated at temperatures higher than calcination.

Claims (8)

1. Procedure for calcining a stream of CaC03 by mixing it with a stream of dense solids superheated at temperatures higher than those of 5 calcination, to produce a CaO stream and a high purity CO2 stream, characterized in that it comprises at least-the following cyclic stages: i) a first stage of generating a stream of dense solids superheated at very high temperature by the oxidation reaction in air of said 10 solids ii) a second stage at a lower temperature where the calcination of the fed CaC03 takes place successively, the reduction with a fuel of the oxidized dense solids that come from the first stage, the separation by segregation of the partially reduced dense solids and of the CaO generated in calcination, and extraction by 15 separated from the product CaO stream and partially reduced dense solids, which are fed to the first stage. iii) use of the CaO current generated in the previous stage 2. Method according to claim 1, characterized in that the first stage is carried out in a circulating fluidized bed. 3. Method according to any one of claims 1-2 characterized in that the second stage is carried out in a circulating raised fluid bed or in a bubbling raised fluid bed. Method according to any one of claims 1 to 3, characterized in that the solid that oxidizes is Fe30 4 that oxidizes to Fe20 3. 5. Method according to any one of claims 1 to 4, characterized in that the first stage operates at temperatures between 950 ° and 12000 C. Method according to any one of claims 1 to 5, characterized in that the second stage operates at temperatures between 870 ° and 950 ° C. Method according to any one of claims 1 to 6, characterized by the division of the second stage into two or more separate and serial sub-stages: eleven

-

a first sub-stage of calcining CaC03 in contact with the superheated dense solids stream, and a second sub-stage of lower dense solids reduction at a lower temperature by reaction with a fuel and subsequent segregation of said dense solids with respect to

5 CaO product of calcination. Method according to any one of claims 1 to 7, characterized in that the generated CaO current is used to feed a clinker kiln of a cement plant. Method according to any one of claims 1 to 7, characterized in that the generated CaO current is used in CO2 capture systems that make use of the CaO reaction with the CO2 diluted in a gas.