STUDIES ON NUCLEAR COAL GASIFICATION IN ARGENTINA

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1 STUDIES ON NUCLEAR COAL GASIFICATION IN ARGENTINA D. Nassini (1), G.G. Fouga (1,2), G. De Micco (1,2) H.E. Nassini (2) and A.E. Bohé (1,2) (1) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina (2) Complejo Tecnológico Pilcaniyeu, Comisión Nacional de Energía Atómica (CNEA), Argentina Contact adress: dnassini@cab.cnea.gov.ar

2 INTRODUCTION A renewed interest on the gasification of solid carbonaceous fuels is emerging since it offers the potential of a cleaner and more efficient energy compared with conventional combustion processes. Gasification refers to a thermo-chemical process that converts solid carbonaceous fuels into either fuel gas (containing CH 4 and some N 2 usually) or syngas (containing mainly H 2 and CO). Gasification involves the possibility of co-generation of electricity and high-value chemicals and fuels in the same energy complex, and the use of a wide range of feed stocks including low-cost fuels like petroleum coke, biomass and municipal wastes. Nuclear gasification defines a process that uses nuclear energy for providing indirect heating to the gasification reactors in order to replace the partial combustion of the feed material that is needed to drive the endothermic gasification reactions.

3 RESEARCH ACTIVITIES ON NUCLEAR COAL GASIFICATION IN ARGENTINA A High Temperature Gas Reactor with 950ºC gas outlet temperature and intermediate circuit is being evaluated as process heat source for the gasification of domestic solid carbonaceous fuels (sub-bituminous coal, asphaltites and petroleum coke). Gasification is a two-step process. In the first step, pyrolysis, volatile components of solid fuels are rapidly released at temperatures between 300 and 500ºC, leaving residual char, which is compound by fixed carbon and mineral matter. The second step, char conversion, involves the gasification of residual char that is much slower than the pyrolysis step and, then, becomes the rate-limiting step. The proposed conceptual design of the nuclear-assisted gasifier involves the decoupling of the pyrolysis (devolatilization) and gasification reactions in two separate Volatile components reactors. Fuel gas Solid Since all chemical PYROLYSIS reactions are closely related to form a complicated reaction network, fuels Char GASIFICATION Or Syngas the two-stage gasification process allows to separate and reorganize one or some of the reactions, promoting the beneficial interactions and inhibiting the undesired ones or isolating the different reaction products.

4 Aromaticscontaining Tar + Pyrolysis gases Solid carbonaceous Fuel IAEA s Technical Meeting on Operating Experience with, and Project Feasibility of TWO-STAGE GASIFICATION REACTOR CONCEPT Pyrolyzer (Fluidized bed pyrolysis reactor) Char Gasifier (Fluidized bed gasification reactor) Product gas Heat from the Nuclear Reactor Fluidized gas Hot coal ash (with un-reacted char) Reagent (steam, CO 2 ) Compared with the conventional gasification technologies, the two-stage gasification concept makes full use of the high-value aromatic compounds contained in the solid fuels so it can co-produce tar and fuel gas or syngas to realize the concept of poly-generation.

5 EXPERIMENTAL PROGRAM Objective: To characterize the behaviour of Argentine solid carbonaceous fuels under typical pyrolysis and gasification conditions, for identifying the most suitable operational parameters in nuclear-assisted two-stage gasifiers. Scope: Theoretical and experimental studies on laboratory scale designed to get the necessary information about the fundamental mechanisms and kinetic parameters of pyrolysis and gasification reactions.

6 EXPERIMENTAL PROGRAM FIRST STEP: We have being making the PYROLYSIS TESTS of three solid carbonaceous fuels coming from Patagonia mines (E,RT,F) in Argentina. The different obtained chars have being prepared though a varied pyrolysis conditions and the effects on the microstructure and on the gasification reactivity of the chars have being researched. Also, the yield and the composition of the evolved tar and pyrolysis gas have being determined. The pyrolysis conditions investigated are: temperature heating rate holding time at the peak temperature

7 EXPERIMENTAL SETUPS FOR PYROLYSIS DROP TUBE FURNACE: To reproduce the real pyrolysis conditions in large-scale gasifiers (high heating rates, short residence time and intense gas convection around individual char particles). Drop Tube Furnace Pyrolyzer

8 EXPERIMENTAL SETUPS FOR PYROLYSIS FIXED BED REACTOR: To reproduce a better controlled pyrolysis reaction to study the effects of the different conditions and the composition of the volatile components. For analyzing the volatile components it is necessary to connect a volatile collector in the outflow. Fixed bed pyrolysis reactor Volatile components collector

9 EXPERIMENTAL PROGRAM SECOND STEP: The GASIFICATION TESTS have being done to the chars prepared in the first step. The principal endothermic gasification reactions studied are: Gasification with CO 2 (Boudouard reaction): C + CO 2 2 CO H = KJ/mol Gasification with steam (water-gas reaction): C + H 2 O CO + H 2 H = KJ/mol After determining the experimental conditions for the chemical control regime of gasification reactions in the different experimental setups, the effects of the following parameters are investigated: Reaction temperature: ºC Gasifying agent partial pressure: 30-80% v/v Char formation conditions: low heating rates, high heating rates

10 EXPERIMENTAL SETUPS FOR GASIFICATION THERMOGRAVIMETRIC ANALYSIS SYSTEM: To follow the kinetic of gasification reaction with CO 2 by measuring the temporal evolution of relative mass changes of the char. The gasification rate, R, under several experimental conditions is evaluated as: m0 mt () α() t = m m 0 where α(t) is the reaction degree (ranging from 0 to 1) at time t, m 0 is the initial char mass, m(t) is the char mass at time t, and m ash is the mass of ash (residual mass at the end of the gasification reaction). Then, the gasification rate can be obtained by derivating the former equation with respect to time: 0 ash dα 1 dm R = = dt ( m m ) dt ash

11 EXPERIMENTAL SETUPS FOR GASIFICATION TUBULAR REACTORS, COUPLED WITH a gas sensor that can quantify the amount of generated CO. It can be A GAS CROMATOGRAPH OR AN IR SPECTROMETER. The gasification reaction kinetic is characterised from the peak areas corresponding to CO(g) concentration. The gasification degree, α, can be defined as: where n CO (t) is the number of CO(g) moles formed from the beginning of the reaction until time t, and n CO (t total ) is the number of total moles formed during the whole reaction.

12 EXPERIMENTAL SETUPS FOR GASIFICATION TUBULAR REACTORS COUPLED WITH A GAS CROMATOGRAPH AND FTIR The gasification with steam needs a more complex experimental setup: a steam generator, a gasification reactor and a water condenser; coupled in series with GC and FTIR. This reaction can be followed either by quantifying the CO or the H 2.

13 GASEOUS COMPONENTS ANALYSIS SETUP Gas cell Gas Chromatograph SRI Instruments Model 8610C Carrier: Ar TCD: H 2 Infrarred Spectrometer Spectrum 400 METANIZER-FID: CO, CO 2 PerkinElmer CO, CO 2

14 PYROLYSIS TESTS THE MOST IMPORTANT RESULTS Pyrolysis heat treatments at temperatures above ºC are observed to produce a significant reordering of the carbonaceous char matrix, increasing the crystalline carbon fraction and decreasing their reactivity. Char reactivity was observed to depend strongly on both: the properties of the solid fuel raw material and its formation conditions, in particular on the timetemperature history of individual fuel particles during pyrolysis. As-received asphaltite sample Asphaltite char after pyrolysis at 950ºC during 60 minutes

15 GASIFICATION TESTS Comparison between the three Argentina carbonaceous fuels H 2 O GASIFICATION CO 2 GASIFICATION These results show that Argentinean solid carbonaceous fuels tested are amenable to be gasified since their reactivities are comparable with those of low-rank coals used in large-scale gasifiers.

16 CONCLUDING REMARKS Nuclear coal gasification is being evaluated as an alternative to provide process heat for the gasification of domestic solid carbonaceous fuels (sub-bituminous coal, asphaltites and petroleum coke) through a two-stage gasification concept. For this purpose, a theoretical and experimental program on laboratory scale is under way with the objective of characterizing the behaviour of selected feed materials under typical pyrolysis and gasification conditions. The research program included the development of specially-designed experimental setups for gasification using CO 2 and steam as gasifying agents. These studies would allow to get relevant information about the fundamental mechanisms and kinetic parameters of the pyrolysis and the gasification reactions, in order to be used in large-scale gasifier design.

17 Muchas Gracias!!! Thank You very much!!!

18 NUCLEAR SITUATION IN ARGENTINA Nuclear reactors for Power generation: 1. Atucha I- German design-365 MWe 2. Embalse Rio Tercero-Canadian design-740 MWe 3. Atucha II-German design-765mwe ( when it can reach the 100%) They operate with natural Uranium and heavy water. Atucha I start to use enriched Uranium (0.85% of U-235) to improve their performance. Projects: 1. Atucha III-China 2. Atucha IV-China- with enriched U (4%) and light water-1000mwe 3. Carem- Argentina-with enriched U (3.4%) and light water-25mwe-to generate electricity in remote areas. Prototype in Ezeiza. A Project in Formosa province. With modification it can be used for desalinization or provision of heating. Nuclear experimental reactors 1. RA-3- Ezeiza-to produce radioisotopes (Mo, Co)- enriched U (20%) and light water-10mw (T less than 100ºC) 2. RA-6-Bariloche-some kw-to human resource training and to research 3. RA-10 (project)-similar to RA-3 but more modern-with Brasil