studies on nuclear coal gasification in … · studies on nuclear coal gasification ... a renewed...

IAEA´s Technical Meeting on “Operating Experience with, and Project Feasibility of Process Heat Applications”, 23-25 May 2016, Budapest, Hungary

STUDIES ON NUCLEAR COAL GASIFICATION IN ARGENTINA

(1)Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina (2)Complejo Tecnológico Pilcaniyeu, Comisión Nacional de Energía Atómica (CNEA), Argentina Contact adress: [email protected]

D. Nassini(1), G.G. Fouga(1,2), G. De Micco(1,2) H.E. Nassini(2) and A.E. Bohé(1,2)

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 CH4 and some N2 usually) or syngas (containing mainly H2 and CO).

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.


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.

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.

Since all chemical reactions are closely related to form a complicated reaction network, 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.

The proposed conceptual design of the nuclear-assisted gasifier involves the decoupling of the pyrolysis (devolatilization) and gasification reactions in two separate reactors.

Solid fuels PYROLYSIS

Volatile components

Char GASIFICATION Fuel gas

Or Syngas

Pyrolyzer (Fluidized

bed pyrolysis reactor)

Gasifier (Fluidized

bed gasification

reactor)

Hot coal ash (with un-reacted char) Fluidized gas

Aromatics-containing Tar + Pyrolysis gases

Product gas

Reagent (steam, CO2)

Heat from the Nuclear Reactor

Solid carbonaceous Fuel

Char

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.


TWO-STAGE GASIFICATION REACTOR CONCEPT

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.

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


EXPERIMENTAL PROGRAM

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

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.

EXPERIMENTAL SETUPS FOR PYROLYSIS


Volatile components collector Fixed bed pyrolysis reactor

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 CO2 (Boudouard reaction): C + CO2 ↔ 2 CO ∆H = 159.7 KJ/mol • Gasification with steam (water-gas reaction): C + H2O ↔ CO + H2 ∆H = 118.9 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: 800-950 ºC • Gasifying agent partial pressure: 30-80% v/v • Char formation conditions: low heating rates, high heating rates


THERMOGRAVIMETRIC ANALYSIS SYSTEM: To follow the kinetic of gasification reaction with CO2 by measuring the temporal evolution of relative mass changes of the char.

The gasification rate, R, under several experimental conditions is evaluated as:

0

0

( )( )ash

m m ttm m

α −=

−

where α(t) is the reaction degree (ranging from 0 to 1) at time t, m0 is the initial char mass, m(t) is the char mass at time t, and mash 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

1( )ash

d dmRdt m m dtα

= = −−


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 nCO(t) is the number of CO(g) moles formed from the beginning of the reaction until time t, and nCO(ttotal) is the number of total moles formed during the whole reaction.




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 H2.

Gas Chromatograph SRI Instruments Model 8610C Carrier: Ar TCD: H2 METANIZER-FID: CO, CO2

Infrarred Spectrometer Spectrum 400 PerkinElmer CO, CO2

GASEOUS COMPONENTS ANALYSIS SETUP

Gas cell


THE MOST IMPORTANT RESULTS PYROLYSIS TESTS


As-received asphaltite sample

Asphaltite char after pyrolysis at 950ºC during

60 minutes

Pyrolysis heat treatments at temperatures above 500-600ºC 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 time-temperature history of individual fuel particles during pyrolysis.

H2O GASIFICATION


CO2 GASIFICATION

GASIFICATION TESTS Comparison between the three Argentina carbonaceous fuels

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.

CONCLUDING REMARKS

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 CO2 and steam as gasifying agents.


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.

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.


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

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

studies on nuclear coal gasification in … · studies on nuclear coal gasification ... a renewed...

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