Usage of heat obtained by cooling of shaft furnaces of "Trepca" corporation with water steam.

Terziqi, Avni ; Rizaj, Musa ; Kamberaj, Naim 等

Abstract: The lead agglomerate's melting process is accompanied with numerous technical, technological and economic difficulties, including the cooling process of the furnace as well. This paper has been analyzing the possibility of using the heat obtained from the shaft furnace by its cooling with water steam. In order to achieve these aims, alongside with the corresponding scheme, in the paper have been compiled appropriate systems of equations related to mass and heat balances, needed to calculate thermal and technical parameters of the characteristic system's points. The corresponding results have been discussed as well. Effects of this system in increasing of the heat usage coefficient are of interest for the purpose of technological process economizing of shaft furnaces within "Trepca" metallurgical corporation.

Key words: heat usage, furnace, cooling, water.

1. INTRODUCTION

Cooling of Trepca water-jacket furnace till now was made according to half-closed recirculation process, without using heat released from the furnace. In this process grade of water heating is low, and this heat is awkward for use (Agolli 1985). With development and construction perfection of modern metallurgic furnace, increases also demand for use of heat, which is ejected during cooling process. Cooling manner with evaporation distinctly fulfil needs of using heat from melting process in furnace. At evaporation cooling, ejected heat, is in contents of steam and has higher temperature and can be used for other destinations. For usage of this heat of cooling with evaporation, it can be done incubation for developing of burning process in furnace and incubation of sanitary water for needs of lead metallurgy. Decision on utilization of secondary resources behaves depending from economic effects and environmental protection taking in regard to not destroy basement for technologic process.

2. THERMAL SCHEME OF PROPOSED COOLING SYSTEM

In system for cooling elements of shaft furnace, is proposed to apply cooling with steam (PFA--FV). In this process heating is taken from cooler rows of furnace roper where gained water steam is. As we can see from Fig. 1, circular heat water (UNC) gets in cooling process with steam of shaft furnace (PFA-FV), takes one quota of heat and gradually come in circular mixture steam-water (PCAU) where such as gets in barrel-separator (CS). In barrel-separator (CS) is divided steam phase from phase of fluid mixture. Saturated steam continues for further use, whereas fluid phase in shape of circular hot water (UNC), again recirculation and returns in cooling process with steam in shaft furnace (1--PFAFV--2--CS--1).

Quantity of saturated steam that is divided in barrel-separator (CS), goes in exchanger of heat KN1, where is taken a quantity of heat, respectively saturated steam is condensed and again returns in barrel-separator (CS--3 KN1--4--CS). In exchanger of heat KN1 circular cold water gets in, warms up and gets out as circular hot water (UNC) with help of circular pump (PC), (PC--5--KN1--6). Then circular hot water partly goes in exchanger KN2, through line 7 and other part through line 11 in exchanger KN3.

[FIGURE 1 OMITTED]

Exchanger of heat KN2 serves for heating o air, which is used for developing of burning process in furnace. In KN2 is taken a quota of circular hot water and as a circular cold water is returned again in exchanger KN1 (7--KN2--8--5). In exchanger KN2 gets in cold water (AFPF) warms up and as hot ait (ANPF) gets in furnace (9--KN2--10). Meanwhile other of circular hot water gets in exchanger KN3 for heating of sanitary water and returns in exchanger KN1 (11-12-5-6). Sanitary cold water (UFS) which gets in exchanger KN3 warms up and ejects as sanitary hot water (UNS), where goes for further use (13KN3-14). In barrel-separator exists one safety-valve and the funnel for feed with cold water chemically elaborated (UFKP)

3. EQUATION SYSTEM OF TERMIC BALANCE

Depending between parameters in characteristic points of cooling system can be described with energy equation, with equation of consume balance of energy bearers, equation of hydraulic balance and as well with equation of enthalpy changes of energy bearers (Sacadura 1993). Preliminarily should be appropriated values of some heat bearers parameters and some other to be taken from calculation of encycled cooling contour with evaporation: It's supposed that circular water in KN1 and KN2, flow with regimen of known temperatures t5/t6 and t7/t8, respectively UFC with temperature [t.sub.5] = [t.sub.8] = [t.sub.12] and appropriated enthalpy [h.sub.5] = [h.sub.8] = [h.sub.12], whereas circular (UNC) with known temperature [t.sub.6] = [t.sub.7] = [t.sub.11] and with enthalpy [h.sub.6] = [h.sub.7] = [h.sub.11]. Quantity of necessary air for heating (Ga)[5], that gets in exchanger KN2 is known from material balance of furnace and has availability with known temperature of surroundings [T.sub.9] with respective enthalpy [h.sub.9], whereas we suppose that gets out with fixed temperature [T.sub.10] with enthalpy [h.sub.10]. Meanwhile, from thermal and hydraulic calculation of contour of evaporation process in furnace is known that [G.sub.1] = [G.sub.2] = [G.sub.0], [G.sub.3] = [G.sub.4] = DAF whereas [G.sub.9]=[G.sub.10]=[G.sub.a], where is: [G.sub.0]general consume of water in contour; [x.sub.D] = [x.sub.SH2]--real capacity content of steam in coolers and furnace funnels [D.sub.AF]--quantity of steam that is generated in furnace coolers. Afterwards values of water steam enthalpies: h', h'' and h are taken from standard tables for thermo physic water attributes whereas [h.sub.1]=[h.sub.4]=h', [h.sub.2]=h'+ [x.sub.D]h and [h.sub.3]=h". Meanwhile differences of enthalpies are fixed from equation system (Michael, J.; Howard, N. 2004.).

[DELTA][h.sub.1,2] = [X.sub.SH2] h (1)

[DELTA][h.sub.3,4] = h (2)

[DELTA][h.sub.5,6] = [h.sub.6]--[h.sub.5] (3)

[DELTA][h.sub.7,8] = [h.sub.7]--[h.sub.8] (4)

[DELTA][h.sub.9,10] = [h.sub.10]--[h.sub.9] (5)

[DELTA][h.sub.11,12] = [h.sub.12]--[h.sub.11] (6)

[DELTA][h.sub.13,14] = [h.sub.14]--[h.sub.13] (7)

Values of flow rate for characteristic points of system are fixed from equalities as follows:

[G.sub.5] = [G.sub.6] = ([D.sub.AF]' x h)/[DELTA][h.sub.5,6] (8)

[G.sub.7] = [G.sub.8] = [G.sub.a]([DELTA][D.sub.9,10]/[DELTA][h.sub.11,12]) (9)

[G.sub.11] = [G.sub.12] = [D.sub.AF]'x h--Ga x [DELTA][H.sub.9,10]/[DELTA][h.sub.11,12] (10)

[G.sub.13] = [G.sub.14] = [D.sub.AF]'x h--Ga x [DELTA][H.sub.9,10]/[DELTA][h.sub.13,14] (11)

Quantity of heat, with which has available raw material in characteristic points of system is determined according to equation:

[Q.sub.i] = [G.sub.i] [h.sub.i] (12)

Where i=1, 2,3,...,14 is number of characteristic points of system whereas quantity of heat that is transmitted in exchangers of heat is:

[Q.sub.k1] = [G.sub.3] [DELTA][h.sub.3,4] = [G.sub.3] h = [D'.sub.AF] h' (13)

[Q.sub.k2] = [G.sub.a] [DELTA][h.sub.9,10] (14)

[Q.sub.k3] = [Q.sub.k1]--[Q.sub.k2] (15)

4. CALCULATION OF PARAMETERS OF CHARACTERISTIC POINTS OF COOLING SYSTEM

For normal work condition of furnace, value determination of variables of cooling system (Table. 1) based in equation (1) till (15), and accomplishes with help of appropriate program, where preliminarily should be known input data as follows: [t.sub.1]=[t.sub.2]=[t.sub.3]=[t.sub.4]=151,84 [degrees]C; [t.sub.5]=[t.sub.8]=[t.sub.12]=70 [degrees]C; [t.sub.6]=[t.sub.7]=[t.sub.11]=90 [degrees]C; [t.sub.9]=20 [degrees]C; [t.sub.10]=80 [degrees]C; [t.sub.13]=15 [degrees]C; [t.sub.14]=50 [degrees]C; [t.sub.15]=15[degrees]C; h'=640,1 kJ/kg; H"=2749 kJ/kg; h=2109 kJ/kg; [h.sub.5]=293,2 kJ/kg; [h.sub.6]=377,1 kJ/kg; [h.sub.7]=377,1 kJ/kg; [h.sub.8]= 293,2 kJ/kg; [h.sub.9]=19,96 kJ/kg; [h.sub.10]=79,84 kJ/kg; [h.sub.11]=377,1 kJ/kg; [h.sub.12]=293,2kJ/kg; [h.sub.13]=63,3 kJ/kg; [h.sub.14]=209,55 kJ/kg; [h.sub.15]=63.4 kJ/kg; Ga=7,604 kg/s; [p.sub.1]=5,9 bar; [p.sub.2]=5 bar; [p.sub.3]=5 bar; [p.sub.4]=5 bar; [p.sub.5]=2,5 bar; [p.sub.6]=2,25 bar; [p.sub.7]=2,25 bar; [p.sub.8]=2 bar; [p.sub.9]=1,3 bar; [p.sub.10]=1,2 bar; [p.sub.11]=2,25 bar; [p.sub.12]=2 bar; [p.sub.13]=4 bar; [p.sub.14]=3,5 bar; [p.sub.15]=10 bar; [G.sub.0]=119,106 kg/s; [D.sub.AF]=0,375 kg/s and [x.sub.D]=0,0031.

Gained results of variables h, [DELTA]h, G, and Q, and [Q.sub.K1], [Q.sub.K2], [Q.sub.K3], but characteristic points of system depends on temperature values, tensions ad appropriate enthalpies of working mediums on system. Also are depended from factors [G.sub.o], [D.sub.AF] and [x.sub.D], values of which are taken from preliminary calculation which are calculated for different regimes of work in furnace and this values mainly are depended from thermal burdens in furnace. Consequently also quantities of heat that are transmitted in system are depended from thermal burdens on furnace (Gordon 1993), respectively from generated quantity of steam in furnace coolers.

5. CONCLUSION

With warming of furnace air effects of economy of fuel will achieve for melting process in furnace for [Q.sub.K2]= 455 kW as a cause of preliminary air warming, and decreasing of energy costs for warming of sanitary water for [Q.sub.K3]= 336 kW, for requests of industrial complex "Trepca". Gained data can be used for wider technical and economic analyse for eventual applying of this cooling system.

6. REFERENCES

Sacadura, J. (1993). Knowledge for thermal transfer (Initiation aux transferts thermiques, TEC&DOC, ISBN 2-85206-618-1, Paris.

Michael, J.; Howard, N. (2004). Fundamentals of Engineering Thermodynamics, John Wiley, ISBN 0-471-27471-2, Hoboken.

Gordon, M. (1993). Thermal calculation of metallurgical furnace, Metallurgy, ISBN5-229-00711-7, Moskva.

Agolli, F., (1985). Handbook of metallurgical furnace (Metalurgjia e metaleve me ngjyra), Faculty of mining and metallurgy, Mitrovice.

Table 1. Calculated values of thermal parameters of heat bearers

 t h G Q

Nr Sign oC kJ/kg kg/s kW

1 UNQ 151.54 640.10 119.11 76239.75
2 PQAU 151.54 646.64 119.11 77018.45
3 AUN 151.54 2749.00 0.38 1030.88
4 KAU 151.54 640.10 0.38 240.04
5 UFQ 70.00 293.20 9.43 2763.82
6 UNQ 90.00 377.10 9.43 3554.70
7 UNQ 90.00 377.10 5.43 2046.53
8 UNQ 70.00 293.20 5.43 1591.20
9 AFF 20.00 19.96 7.60 151.78
10 ANF 80.00 79.84 7.60 607.10
11 UNQ 90.00 377.10 4.00 1508.16
12 UFQ 70.00 293.20 4.00 1172.62
13 UFQ 15.00 63.30 2.29 145.23
14 UNS 50.00 209.55 2.29 480.78
15 UPK 15.00 63.40 0.01 0.48

Table 2. Exchanged quantity of heat in cooling system

 EXCHANGERS

[K.sub.1] [K.sub.2] [K.sub.3]
[Q.sub.K1] [kW] [Q.sub.K2] [kW] [Q.sub.K3] [kW]
791 455 336