THE POSSIBILITIES OF CO 2 EMISSION REDUCTION IN THE PROCESS OF STEEL CHARGE HEATING THROUGH THE SELECTION OF HEATING RATE

The reduction of carbon dioxide emission is an important aspect of the economic policy of each country. Institutions promoting environmental protection seek to reduce the level of greenhouse gas emissions. One of the main emitters of harmful gases to the atmosphere is the steelmaking sector. The heating technology used in metallurgical works contributes to the amount of emitted carbon dioxide that forms as a result of the loss of steel and the combustion of fuel, whose thermal energy is used during the course of the charge heating process in the heating furnace. Achieving the imposed ecological targets by not exceeding the specified emission level is possible by implementing appropriate pollutant emission reducing technologies in the metallurgical industry. Based on numerical computation results, the effect of heating rate on the emission of carbon dioxide has been determined in the paper. This study demonstrates that by selecting the appropriate steel charge heating technology the emissions of greenhouse gases can be substantially reduced.


INTRODUCTION
An important regulatory issue in environmental protection is the economic instrument of a State's ecological policy in a form of transferable emission allowances.The operation of this mechanism consists of specifying the allowable level of emission in a given area and allocating allowances for this emission to the emitters by the institution responsible for environmental protection, and subsequent trading these allowances by the emitters with one another.
The main cause of the increase in the emissions of greenhouse gases, and especially carbon dioxide, is sought in metallurgical processes taking place in the steelmaking sector [5,6].
Since 2005 the Community Greenhouse Emissions Trading Scheme has been functioning in the European Union.The Scheme has covered the operators of installations associated with the generation of energy; production and processing of nonferrous metals; production of cement clinker, glass and ceramic products; and wood production [5].
By its decision of March 2007, the European Commission reduced Poland's average annual allocation of carbon dioxide emission allowances for the years 2008-2012 from 284.6 mln tons to 208.4 mln tons, of which the limit for the steelmaking sector was reduced from 14.4 to 11.8 mln tons per year [4,6].Moreover, the directive of the European Parliament has introduced an auction mechanism as the primary method of allocating harmful gas emission allowances for the reference period of 2013-2020.The basis for the allocation of free emission allowances in this reference period for sectors subject to emission leakage shall be emission factors.The steelmaking sector has been classified into sectors that are considerably endangered by a high emission risk level.
The implementation of regulations on the standards for emissions from installations for metallurgical enterprises encourages the proecological investment projects to be carried out, but also creates the need for purchasing additional carbon dioxide emission allowances, which contributes to the increase in competitiveness in the steelmaking sector [5].It is noteworthy that by using appropriate greenhouse gas reduction technologies, the steelmaking industry could achieve the ecological goal of not exceeding the specified emission level.This paper shows how the selection of the appropriate steel charge heating technology can contribute to the reduction of the carbon dioxide emission.

THE OBJECT OF MODELLING
The object of modelling is a pusher heating furnace (Figure 1) [3].It was assumed that the heating chamber of the furnace was represented by a rectangular prism with a length of L = 28 m, a height of 2H = 2.6 m, and a width of B = 5.6 m.Also, the furnace was conventionally divided into 20 calculation zones and 5 technological zones [1,2].
For computation purposes, the pusher furnace was reduced to a simple model, in which the charge moves along the furnace chamber over the length L with uniform motion countercurrently to the direction of furnace gas movement.It was assumed that the transfer of heat to the charge takes place bilaterally over the whole length L. In view of the assumed symmetry of the phenomena, only heat exchange in the zones above the charge axis is considered.The furnace was assumed to be furnished with a recuperator.

NUMERICAL COMPUTATION OF CHARGE HEATING
In order to perform computer simulation of the effect of heating rate on heat consumption and steel loss, a mathematical model for charge heating and heat exchange in the chamber of a pusher furnace was developed [2,3].
For the numerical computation of charge heating, the elementary balances method was used, and for the computation of the temperature field in the furnace chamber -the brightness and configuration ratios method [2,4].
The method of supplementary temperature was used to calculate the loss of steel.The loss of steel in every compartment of time was marked was according to the dependence: where: The increment in steel loss in time τ ∆ was determined from the formula: where: A -constant value.
The fuel (natural gas) volume flux for an arbitrary computational zone i was determined from the relationship: where: The increment in steel loss in time   was determined from the formula:

4) where:
A -constant value.The fuel (natural gas) volume flux for an arbitrary computational zone i was determined from the relationship: The heat flux fed to the computational furnace zone i was determined from the relationship: The numerical computation of heat consuption of the furnace chamber was computed using the zone balances method.The unit heat consumption was calculated from the equation: The useful heat flux for the i-th computational zone was determined from the formula: The heat flux carried out with scale was computed from the equation: The heat flux carried away with sliding rail cooling water was computed from relationships given in work [7], whose general form is described by the equation: The heat flux lost by the furnace lining was computed from the equation: The heat flux lost by radiation through the open furnace doors and openings was determined from the relationship: The heat flux fed to the computational furnace zone i was determined from the relationship: The numerical computation of heat consumption of the furnace chamber was computed using the zone balances method.The unit heat consumption was calculated from the equation: relationship: The heat flux fed to the computational furnace zone i was determined from the relationship: The numerical computation of heat consuption of the furnace chamber was computed using the zone balances method.The unit heat consumption was calculated from the equation: The useful heat flux for the i-th computational zone was determined from the formula: The heat flux carried out with scale was computed from the equation: The heat flux carried away with sliding rail cooling water was computed from relationships given in work [7], whose general form is described by the equation: The heat flux lost by the furnace lining was computed from the equation: The heat flux lost by radiation through the open furnace doors and openings was determined from the relationship: In computations, also a constant value of other losses was assumed, and the heat input from the exothermic metal oxidation reaction was allowed for: The useful heat flux for the i-th computational zone was determined from the formula: -constant value.e fuel (natural gas) volume flux for an arbitrary computational zone i was determined from the ationship: (3.5) e heat flux fed to the computational furnace zone i was determined from the relationship: e numerical computation of heat consuption of the furnace chamber was computed using the zone lances method.The unit heat consumption was calculated from the equation: e useful heat flux for the i-th computational zone was determined from the formula: The heat flux carried out with scale was computed from the equation: The heat flux carried away with sliding rail cooling water was computed from relationships en in work [7], whose general form is described by the equation: The heat flux lost by the furnace lining was computed from the equation: The heat flux lost by radiation through the open furnace doors and openings was determined m the relationship: computations, also a constant value of other losses was assumed, and the heat input from the othermic metal oxidation reaction was allowed for: The heat flux carried out with scale was computed from the equation: (3.4) here: -constant value.he fuel (natural gas) volume flux for an arbitrary computational zone i was determined from the lationship: (3.5) he heat flux fed to the computational furnace zone i was determined from the relationship: he numerical computation of heat consuption of the furnace chamber was computed using the zone lances method.The unit heat consumption was calculated from the equation: he useful heat flux for the i-th computational zone was determined from the formula: The heat flux carried out with scale was computed from the equation: The heat flux carried away with sliding rail cooling water was computed from relationships ven in work [7], whose general form is described by the equation: The heat flux lost by the furnace lining was computed from the equation: The heat flux lost by radiation through the open furnace doors and openings was determined om the relationship: (3.12) computations, also a constant value of other losses was assumed, and the heat input from the othermic metal oxidation reaction was allowed for: The heat flux carried away with sliding rail cooling water was computed from relationships given in the work [7].Its general form is described by the equation: The heat flux lost by the furnace lining was computed from the equation: fuel (natural gas) volume flux for an arbitrary computational zone i was determined from the tionship: (3.5) heat flux fed to the computational furnace zone i was determined from the relationship: numerical computation of heat consuption of the furnace chamber was computed using the zone ances method.The unit heat consumption was calculated from the equation: (3.7) useful heat flux for the i-th computational zone was determined from the formula: The heat flux carried out with scale was computed from the equation: The heat flux carried away with sliding rail cooling water was computed from relationships en in work [7], whose general form is described by the equation: The heat flux lost by the furnace lining was computed from the equation: The heat flux lost by radiation through the open furnace doors and openings was determined m the relationship: (3.12) computations, also a constant value of other losses was assumed, and the heat input from the thermic metal oxidation reaction was allowed for: The heat flux lost by radiation through the open furnace doors and openings was determined from the relationship: (3.4) here: -constant value.he fuel (natural gas) volume flux for an arbitrary computational zone i was determined from the lationship: (3.5) he heat flux fed to the computational furnace zone i was determined from the relationship: he numerical computation of heat consuption of the furnace chamber was computed using the zone alances method.The unit heat consumption was calculated from the equation: he useful heat flux for the i-th computational zone was determined from the formula: The heat flux carried out with scale was computed from the equation: The heat flux carried away with sliding rail cooling water was computed from relationships iven in work [7], whose general form is described by the equation: The heat flux lost by the furnace lining was computed from the equation: The heat flux lost by radiation through the open furnace doors and openings was determined om the relationship: (3.12) computations, also a constant value of other losses was assumed, and the heat input from the xothermic metal oxidation reaction was allowed for: In computations, also a constant value of other losses was assumed, and the heat input from the exothermic metal oxidation reaction was allowed for: he increment in steel loss in time   was determined from the formula: (3.4) here: -constant value.he fuel (natural gas) volume flux for an arbitrary computational zone i was determined from the elationship: (3.5) he heat flux fed to the computational furnace zone i was determined from the relationship: he numerical computation of heat consuption of the furnace chamber was computed using the zone alances method.The unit heat consumption was calculated from the equation: he useful heat flux for the i-th computational zone was determined from the formula: The heat flux carried out with scale was computed from the equation: The heat flux carried away with sliding rail cooling water was computed from relationships iven in work [7], whose general form is described by the equation: The heat flux lost by the furnace lining was computed from the equation: The heat flux lost by radiation through the open furnace doors and openings was determined rom the relationship: (3.12) n computations, also a constant value of other losses was assumed, and the heat input from the xothermic metal oxidation reaction was allowed for: The balance of energy for different losses of warmth should also be considered .The losses are different for different levels of furnace efficiency.

Influence of heat consumption on the CO 2 emission
The emission of carbon dioxide is directly connected with coefficient of unitary heat con-sumption as well as indirectly with the loss of steel [3,4].
It the emission of carbon dioxide in the dependence from the value of heat consumption (the q) can be calculated from the equation: You in balance of energy to consider different losses of warmth also sho different to accept as solid or to become addicted him from efficiency of furna

REDUCTION OF CO2 EMISSION IN THE PROCESS OF STEEL CHA
Influence of heat consumption on the CO2 emission The emission of dioxide of carbon is connected with coefficient of unitary h as well as indirectly with loss of steel on scale [3,4].It the emission of dioxide of carbon in dependence from value of heat consu count with dependence: The variation of charge surface temperature during the heating period is de general equation: The analysis covered three heating technologies defined by the value of the e G=0,6).It it was accepted was, that:  composition of earth gas: CO2 -0,1 %, O2 -0,1 %, CH4 -96,7 %, C2H6 -0  the gas calorific value Wd= 34302, kJ/um 3 gazu,  specific mass of CO2 in conventional conditions ρ0= 1,94 kgCO2/um 3 g,  the unit volume of dioxide of carbon during burning with value of relat α=1,05 carries out Based on the adopted assumptions and calculations made, the emission of c been determined for selected heating technologies.The results are given in Ta The analysis of the obtained results shows that carbon dioxide emission is d heat consumption index.Changing over technologies from G=1.0 to G=0.6 c consumption for respective heating rates, thus resulting in an increase in noticed that high effects of heat consumption reduction, and thus CO2 emissi about by conducting the heating process at appropriate heating rates.Changi rate of M = 100 K/h to rational values (M = 500 ÷ 600 K/h) will result in a c carbon dioxide emission.
The variation of surface temperature charge during the heating period is described by the following general equation: The analysis covered three heating technologies defined by the value of the exponent G (G = 1; G = 0.8; G = 0.6).It was assumed that: • composition of earth gas: CO burning with value of relation of air excess the gas α = 1.05 carries V" CO2 = 0.98 m 3 /m 3 g .Based on the adopted assumptions and calculations made, the emission of carbon dioxide (CO 2 ) has been determined for selected heating technologies.The results are given in Table 1.
The analysis of the obtained results shows that carbon dioxide emission is directly related to the unit of heat consumption index.Changing technologies from G = 1.0 to G = 0.6 causes an increase in heat consumption for respective heating rates, thus resulting in an increase in CO 2 emission.It can be noticed that high effects of heat consumption reduction, and thus CO 2 emission reduction, are brought about by conducting the heating process at appropriate heating rates.Changing over from the heating rate of M = 100 K/h to rational values (M = 500-600 K/h) will result in a considerable reduction of carbon dioxide emission.

Influence of steel loss on the CO 2 emission
The acceptable average value of energy consumption of production in Polish metallurgy of iron is about 35 GJ/t.It was calculated for the heating furnace whose heating chamber length was L = 28 m.Heating flat charge has a thickness of 2s = 0.3 m and the length l = 5 m.It was assumed that: • surface of heating charge: A = 300 m 2 , • volume of charge: V = 42 m 3 , • specific mass of charge: ρ = 7850 kg/m 3 , • mass of charge m = ρ .V = 329 700 kg.
Dependence captures in reference loss of steel to mass of heating charge: The loss of heat in reference to mass of lost steel was counted was with dependence: In making calculation, an average energy intensity value of 35 000 kJ/kg was taken.The carbon dioxide emission, as dependent on the steel loss value, was determined from the formula (16).The calculations were made for three heating technologies (G = 1; G = 0.8; G = 0.6).The calculation results for the technology G = 1 are given in Table 2.
The results for carbon dioxide emission, depending on the steel loss value, for the technologies under examination are presented in Table 3.
When analyzing the calculation results it can be noticed that with the increase in steel loss, with the corresponding increase in heat consumption, carbon dioxide emission increases.The values of CO 2 emission through the loss of steel are much lower than those resulting from heat consumption.
The calculation results presented in Table 3 indicate that the value of CO 2 emission at heating rates of M = 600-1000 K/h are nearly identical for each of the heating technologies.Only for the initial heating rates the difference between the heating conducted at the constant surface temperature increase rate (G = 1) and the curvilinear surface temperature variation (G = 0.6) can be seen.
The total carbon dioxide emission, as dependent on the heating rate, for the technologies under analysis is represented in Figure 2.  When examining the results represented in Figure 2 it can be found that depending on the method of operation of heating equipment, at rational heating rates and through the selection of the heating technology, the carbon dioxide emission can be substantially reduced.The calculation results indicate that, from the point of view of both ecological and economic assessment, it is disadvantageous to heat steel charge at loss heating rates (low furnace capacities), as this will result in a considerable increase in CO 2 emission.The lowest CO 2 emission indices were achieved for heating conducted at a constant surface temperature increase rate (G = 1).

SUMMARY
From the performed numerical computations and the analysis of the obtained results, the following conclusions can be drawn: 1.The results of numerical modelling show that for each heating case there is a specific heating rate that assures the minimum heat consumption, steel loss and CO 2 emission.2. The carbon dioxide emission level is directly related to the unit heat consumption index and, indirectly, to the loss of steel.3. The adopted heating technology exhibits a significant influence on the carbon dioxide emission.
Advances in Science and Technology Research Journal Vol. 9 (27) 2015 22 4.The reduction of carbon dioxide emission can be achieved by using rational heating rates (M = 500-600 K/h). 5.The lowest CO 2 emission level is assured by charge heating conducted at a constant surface temperature increase rate, i.e. by using the technology G = 1.

Fig. 2 .
Fig. 2. Effect of the heating rate on the total CO 2 emission for selected technologies

Table 1 .
Results of the calculation of the effect of heating rate on the emis heating technologies, depending on the heat consumption magnitudes

Table 1 .
Results of the calculation of the effect of heating rate on the emission of CO 2 for different heating technologies, depending on the heat consumption magnitudes

Table 2 .
Results of the calculation of the effect of heating rate on the emission of CO 2 , depending on the steel loss value for G = 1

Table 3 .
Results of the calculation of the effect of heating rate on the emission of CO 2 for different heating technologies, depending on the steel loss value