HOT BLAST SOVE I INTRODUCTION Evolution of hot stove  The first heat exchanger worked at 1828 in USA with pipe type, use coal as fuel Hot blast can only be heated up to o 315 C  From now on then, heat exchanger continuously was developed  We can classify: Continuous type : Pipe type, plate pipe discrete type: Hot blast stove I INTRODUCTION Purpose of hot stove in blast furnace plant  To supply hot blast to blast furnace  High hot blast temperatures are essential as they reduce the furnace’s coke requirement substantially  To facilitate the injection of auxiliary fuels such as pulverized coal as a replacement for expensive metallurgical coke  Significant effect in terms of reducing the cost of hot metal I INTRODUCTION Hot stove’s types I OPERATION OF HOT STOVE  Fuel of hot stove  Hot stove use the blast furnace gas, coke oven gas and air to burn together  The hot gas with high temperature will be mix with cold air to control temperature before it go to blast furnace  To keep the hot gas continuously supplies to blast furnace, we need at less two hot stoves I OPERATION OF HOT STOVE  Operation On- gas On- blast II.STRUCTURE STRUCTURE OF DME TYPE        TWO CHAMBER BURNER DOME REFRACTORY CHECKER BRICK CAST IRON GRID HYDRAULIC TANK II.STRUCTURE TWO CHAMBER Combustion chamber  Combustion chamber Place to burn fuel Checker chember having checker brick for absord, release, store heat  checker chamber II.STRUCTURE BURNER Burner have two hole, one for fuel (BFG + COG), one for air Ceramic burner make by refractory, brick grade HA65/S65KB Fuel and air will be mixed inside ceramic burner and burned in top of burner(outside ceramic burner BFG+COG AIR II.STRUCTURE DOME FOR HOT STOVE III.PREAHEATING EXCHANGER III.1 The heat recovery system with heat carrier medium (using Oil) III.1 The heat recovery system with heat carrier medium (using Oil)  Advantages Control the temperature of  Preheat combustion gas and air  Inlet chimney Through this oil service station  Disadvantages  Very complicated due to the addition of oil service station (pumps, discharge tank…)  The oil is only able to operate at temperature lower than 350 0C III.PREAHEATING EXCHANGER III.2 The heat recovery system without heat carrier medium III.2 The heat recovery system without heat carrier medium  Advantages  Very simple when we don’t need to use the oil service station  The hot blast temperature control is simpler by bypass valve  Disadvantages  Cost for piping increase  The inlet temperature of chimney is slightly higher than the system with heat carrier medium III.PREAHEATING EXCHANGER III.3 The heat recovery and preheating system III.3 The heat recovery and preheating system  Advantages  Optimize save energy by combining the heat recovery and preheating system  Not restricted in preheating capacity of system to the temperature limitation  Disadvantage  Add more cost for installation of gas fire heat exchanger IV OPERATION MODE The stove system can operate in two different modes:  Cyclic mode  Parallel mode with N = 2, the system only can operate with cyclic mode With N > 2, the system can operate with either cyclic mode or parallel mode IV.OPERATION MODE General formula θ = θh + Δθ + θc = N x ( θc – rθc) θc(N- N*r -1) = θh + Δθ • • θ: period blast Δθ: HS changing time • θh : on gas time • θc : on blast time • • r: overlap factor N: amount of HS IV.OPERATION MODE Cyclic mode The cyclic mode with one stove on blast and the remaining stove being reheated  Formula: θh+Δθ = 2θc With r =0, N = IV.OPERATION MODE Parallel mode  The parallel mode with two stove on blast at different temperature and two stove be reheated  Formula: θh+Δθ = θc with N =4, r = 0.5) IV.OPERATION MODE conclusion    In general, we choose cyclic mode or parallel mode with mainly reason for safety When HS system operate with parallel mode( N =4), fourth acting as a back up while repairing or replacing If one of four stove fail, the system will operate with stove with cyclic mode V STRESS CORROSION CRACK (SCC) PHENOMENON a NOx  Cause: At temperature ≥ 1300oC, NOx increase exponentially  Phenomenon treatment: The heat storage level should be designed in a way with the lowest possible dome temperature V SCC PHENOMENON Comment: The differential temperature between hot blast temperature hot blast temperature and dome temperature is 100 0C to 150 C In cyclic mode the start point temperature of hot blast is higher than parallel mode so that it’s easier to produce NOx V SCC PHENOMENON b The penetration of NOx into the shell Cause: NOx penetrate into shell, the temperature reach to 180 C, it happen the condensation of mixture of NOx and H2O NOx + H2O  Acid NOx from N2, O2 H2O from air, BFG Phenomenon treatment: Whole shell receives an external insulation to keep the temperature shell above 180 C Whole shell receives an internal acid resistant coating V SCC PHENOMENON c Stress concentration Cause: The dome construction is vault construction so tensile stress concentration will appear maximum at the dome of hot stove Phenomenon treatment: Shell should be manufactured from stress corrosion resistant steel Welds and notches on the inner surface of the shell must be minized [...]... During hot stove operation, its always happen expansion, oil tank will control automatic amount of oil to support combustion chamber III.PREAHEATING EXCHANGER (HEAT RECOVERY SYSTEM)  Purpose of heat recovery system:  Used for purpose of save energy by means of utilization of low calorific combustion gas (BFG) and waste gas (for preheating the combustion gas)  Increase combustion efficiency for hot stove. .. blast time • • r: overlap factor N: amount of HS IV.OPERATION MODE Cyclic mode The cyclic mode with one stove on blast and the remaining stove being reheated  Formula: θh+Δθ = 2θc With r =0, N = 3 IV.OPERATION MODE Parallel mode  The parallel mode with two stove on blast at different temperature and two stove be reheated  Formula: θh+Δθ = θc with N =4, r = 0.5) IV.OPERATION MODE conclusion    In general,... one of four stove fail, the system will operate with 3 stove with cyclic mode V STRESS CORROSION CRACK (SCC) PHENOMENON a NOx  Cause: At temperature ≥ 1300oC, NOx increase exponentially  Phenomenon treatment: The heat storage level should be designed in a way with the lowest possible dome temperature V SCC PHENOMENON Comment: The differential temperature between hot blast temperature hot blast temperature...II.STRUCTURE REFRACTORY FOR HOT STOVE Different temperature working area we item will be installed different material of position Refractory and checker brick 45% 4 burner 1 refractory Al2O3 75% To avoid thermal shock 5 2 3 3 6 4 7 8 Hot blast outlet Upper part Dome 5 Upper part 2 Al2O3 95.5% Silica 95.5% Silica 95.5% Silica 6 45%... receives an internal acid resistant coating V SCC PHENOMENON c Stress concentration Cause: The dome construction is vault construction so tensile stress concentration will appear maximum at the dome of hot stove Phenomenon treatment: Shell should be manufactured from stress corrosion resistant steel Welds and notches on the inner surface of the shell must be minized ... Used for purpose of save energy by means of utilization of low calorific combustion gas (BFG) and waste gas (for preheating the combustion gas)  Increase combustion efficiency for hot stove  Help the hot blast temperature to reach approx 1250~13000C without enrichment gas  Control the inlet temperature of chimney III.PREAHEATING EXCHANGER III.1 The heat recovery system with heat carrier medium (using... III.2 The heat recovery system without heat carrier medium III.2 The heat recovery system without heat carrier medium  Advantages  Very simple when we don’t need to use the oil service station  The hot blast temperature control is simpler by bypass valve  Disadvantages  Cost for piping increase  The inlet temperature of chimney is slightly higher than the system with heat carrier medium III.PREAHEATING... temperature V SCC PHENOMENON Comment: The differential temperature between hot blast temperature hot blast temperature and dome temperature is 100 0C 0 to 150 C In cyclic mode the start point temperature of hot blast is higher than parallel mode so that it’s easier to produce NOx V SCC PHENOMENON b The penetration of NOx into the shell Cause: NOx penetrate into shell, the temperature reach to 0 180 C, it... and preheating system  Not restricted in preheating capacity of system to the temperature limitation  Disadvantage  Add more cost for installation of gas fire heat exchanger IV OPERATION MODE The stove system can operate in two different modes:  Cyclic mode  Parallel mode with N = 2, the system only can operate with cyclic mode With N > 2, the system can operate with either cyclic mode or parallel