P r o c e e d i n g s o f t h e 4 t h U l c o s s e m i n a r , 1 - 2 O c t o b e r 2 0 0 8 SP12 - New Direct reduction / n°4-9
Biomass gasification for DRI production
Thomas Buergler1 and Antonello Di Donato2
Voestalpine Stahl GmbH, Linz, Austria & 2 Centro Sviluppo Materiali SpA, Roma, Italy
The Direct Reduction process can be carried out using syngas from biomass. Mathematical models of the inte- grated process gasification plus direct reduction have been used to evaluate flow rate, temperature and compo- sition of the gas in the various steps of the whole process. Fluidised bed gasification and operation with tech- nological oxygen at high pressures is the proposed solution to produce syngas. Best candidates for such appli- cation are biomass from forest and wood industry and agricultural residues. Both of such type of biomass are present and distributed in many European areas in such amount to make industrially possible their use, taking into account the logistic requirements. A cost between 30-60 €/t DRI is roughly estimated. The characteristics of the syngas implies the adoption of purification steps, before the use of the syngas in the shaft furnace, using technologies permitting hot gas cleaning, to save energy efficiency of the process.
composition and gasification conditions, in particular: feedstock feeding rate, O2 and steam flow rates.
Direct Reduction processes for a promising ways to reduce
producing DRI is
steelmaking industry, maintaining high ductivity and steel quality. Moreover
produced methane, bility and
starting from different energy source, like coal, biomass, waste. This increases flexi- applicability of the process to different
contexts and different energetic ticular the DRI production using
scenarios. In syngas from
In a second step, flow rate and composition of the syngas, calculated by the gasifier model, have been used as input for mathematical models of mass and energy balance of the integrated process.
Mass and energy balance calculations have been used to evaluate the biomass consumption and CO2 production in process schemes of integrated cycles biomass gasifier plus direct reduction reactor.
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Modelling biomass based DRI production
The evaluation of feasibility of DRI production from biomass syngas has been carried out in the first phase of the ULCOS project.
The feasibility study has been carried out by means of mathematical models of the integrated process gasification plus direct reduction.
A number of possible configurations of the integrated process have been considered, including gas purifica- tion units, gas re-heating steps, gas re-cycling.
The simulations indicate that the global performance of the process depends on the cycle configuration, type and number of implemented purification units, and important process parameters like heat losses of the reactors and temperature of the gas entering the direct reduction reactor.
For this purpose, a mathematical model of the gasifi- cation step has been first developed.
The model assumes that gasification is a staged process subdivided in five different steps: pyrolysis, volatiles combustion, char combustion, char gasifica- tion and equilibrium reactions. Oxygen and steam are used as gasifying gases.
Representative result of the model simulations is a consumption of 650 kg biomass (no additional fossil fuel), to be gasified with a mixture O2/steam, for the production of 1 t of DRI.
Mass and energy balance of the integrated cycle, starting from a simulated syngas from biomass gasi- fication, has been also supplied by HYL.
Kinetic parameters of pyrolysis and char combustion have been found in literature [1,2,3]. The model gives results in agreement with available experimen- tal data of gas composition in fluidized bed with biomass from wood industry and agricultural resi- dues.
Figure 1 shows an example, based on HYL direct reduction process. In the simulation 600 kg of bio- mass (wood residues) generates 101140 m3(STP)/h of a syngas, which is used to produce 100 t/h of DRI.
Consequently the gasifier model has been considered suitable for predicting the composition of the syngas generated by the gasifier as a function of feedstock