Mathematical Optimization of Ironmaking with Biomass as Auxiliary Reductant in the Blast Furnace

Abstract

The potential of using biomass in ironmaking is investigated by simulation. Biomass is used to partially replace fossil reductants in the blast furnace process, which is described mathematically by a thermodynamic model. The model is cast in linear form to facilitate an efficient economic optimization of the production of raw steel, considering costs of raw materials, energy and CO 2 emissions of the unit processes up to the basic oxygen furnace. The high oxygen content and low heating value of biomass makes it necessary to study a possible external pyrolysis of it prior to injection into the furnace. The economy of biomass injection and its dependence on the price structure of raw materials and emissions are investigated. The results throws light on how the prices of biomass and emission rights, compared to the price of coal and coke, affect the optimal biomass pre-processing (pyrolysis) and injection rate.KEY WORDS: ironmaking blast furnace; biomass injection; pyrolysis; optimization; CO 2 emissions. The basic oxygen furnace (BOF) converts the hot metal (hm) produced in the blast furnace into raw steel (rs). Neglecting other additives than scrap, which for the sake of simplicity was assumed to be pure Fe, the mass flow of raw steel and the volume flow rates of oxygen (consumed in) and off-gases (produced in) the BOF can be written where j 1 is obtained from the iron balance equation, and j 2 and j 3 from the carbon balance equation. Biomass Pre-processingWood chips, forest slash or logging residues are potential non-fossil sources of energy and reduction potential in the ironmaking process. 8) However, as pointed out by other investigators 5) and also demonstrated by the present authors in earlier simulation analysis, 7) injection of dry wood chips results in a low coke replacement ratio. A key issue is that the high oxygen content of the biomass, combined with the low heating value, results in low flame temperature and decreased productivity. A possible remedy is to pre-process the biomass into a form that is better suited for injection into the blast furnace 5,6) : A (partial) pyrolysis of the biomass prior to injection would lower its oxygen content, but naturally also decreases the yield (h) due to loss of valuable components, such as carbon and hydrogen. The asterisks ( * ) in Fig. 2 illustrate a typical dependence of yield and composition on the pyrolysis temperature.9) In order to express the variables for arbitrary pyrolysis temperatures, piecewise cubic hermite interpolating functions were adapted to the values within the temperature interval T pyro ϭ(150°C, 800°C), resulting in the curves depicted in the figure. Furthermore, the effective heating value of the biomass (H bio ) was estimated from reported values and approximated as function of the pyrolysis temperature (cf. Fig. 2). For the sake of simplicity, by-products of the pyrolysis units (e.g., tar, gases) were neglected, but so was also the energy needed to maintain the elevated pyrolysis temperatures. ISIJ International, Vol. 49 (2009) Blast ...

Novel Approach Towards Biomass Lignin Utilization in Ironmaking Blast Furnace

“…Intensive work is being done to mitigate the CO 2 emissions in steel industry by partial substitution of fossil fuels (coal and coke) with renewable source of energy such as biomass. [7][8][9][10][11][12][13][14][15] One of biomass materials which could be used as binder for briquettes and reducing agent in blast furnace is lignin. Lignin is considered as the second most abundant renewable biomass on the earth after cellulose and it represents about 30% of the total raw biomass.…”

Optimization of Top Gas Recycling Conditions under High Oxygen Enrichment in the Blast Furnace

“…5) As expected, the costs of CO 2 emissions and stripping/storage were found to affect the optimal degree (b) of top gas recycling, with lower values of b at higher stripping cost, and maximum recycling at higher costs of emissions. In the following, some examples have been chosen to illustrate the optimal states of the system, with the emission and stripping/storage costs reported in Table 3.…”

“…We study the units in an integrated steel works from the raw material processing units through one blast furnace to the basic oxygen furnace (BOF), 5) with liquid steel as the main product (Fig. 1).…”

“…Instead, new innovative processes or sources of energy, or fundamentally new ways of operating existing unit processes have to be found. 2) In order to suppress the emission rates, the use of non-fossil reductants, e.g., biomass, [3][4][5] BF top gas recycling 2,[6][7][8][9] and CO 2 capture and storage 10) have been proposed as potential solutions. Even though top gas recycling in the blast furnace is an old idea, and has been practiced already in the 1980'es in several campaigns at Toulachermet in Russia, 11) the awakened interest in the technique is due to the potential of suppressing the coke rate and dramatically reduce emissions if the stripped CO 2 can be stored.…”

Improved Energy Efficiency and Fuel Substitution in the Iron and Steel Industry

“…(Helle et al, 2010;Helle et al, 2009;Gupta, 2003;Suopajärvi and Fabritius, 2012; . Helle et al (2010) and Helle et al (2009) simulated partial substitution of fossil reducing agents with biomass in the BF. They concluded that the biomass had to be pre-processed through pyrolysis, because the high oxygen content and low heating value of raw biomass would reduce the productivity of the BF.…”