Methods for increasing the energy-efficiency of glass furnaces

Abstract

Methods for increasing the heat efficiency of commercial glassmaking are examined for the example of an analysis of the heat-balance in glass furnaces with a horseshoe flame. It is shown that it is possible to develop container-glass furnaces with world-class energy efficiency.The energy efficiency of glass furnaces is determined by the specific heat consumption per 1 kg melt:where q sp is the specific heat consumption, kJ/kg; B is the fuel consumption rate, m 3 /sec; Q low w is the lower working calorific value of the fuel, kJ/m 3 ; P fc is the furnace capacity, kg/sec; and, Q elec is the electric heating power (Q elec = 0 for a flame furnace), kW. In world practice, the highest energy efficiency of container glassmaking was achieved in regenerative furnaces with a horseshow flame: q sp » 3.85 -4.33 MJ/kg (920 -1035 kcal/kg). Domestically manufactured furnaces are characterized by considerably higher specific heat consumption for glassmaking. For this reason, the most important problem facing the industry is to increase the energy efficiency of furnaces. Its urgency is especially evident in the present environment of increasing natural gas and electricity prices.We shall examine the conditions under which worldlevel energy efficiency of industrial glassmaking is attained for the example of a regenerative flame furnace (Q elec = 0).In its general form the equation of heat balance in the working space of a continuous, flame, glass furnace (heat accumulation in masonry Q 6 = 0) heated by gas or liquid fuel (the underburning of solid fuel Q 4 = 0) has the form Q chem + Q p.air + Q p.f = Q 1.1 + Q 1.2 + Q 2 + Q 3 + Q 5 + Q negl , (2) where Q chem = BQ low w is the chemical heat of the fuel, kW;Q p.air = Bc a t a L a is the physical heat of heated air, kW; Q p.f = Bc f t f is the physical heat of the fuel, kW; Q 1.1 is the heat consumption for glassmaking, kW; Q 1.2 = c mg t mg P loss are the heat losses with the production melt flow, kW; Q 2 = Bc s t s V a are the heat losses with the products of fuel combustion, kW; Q 3 = 0.02BQ low w is the chemical underburning of the fuel, kW;are the heat losses by heat conduction through the masonry and by radiation through the burner inlets, doghouse roofs, and closed observation windows (2nd term), kW; Q negl = 0.1(Q 1 + Q 3 + Q 5 ) are the neglected heat losses; c a , c f , and c s are the specific heat capacity of air, fuel, and smoke, respectively, kJ/(m 3 × K); t a , t f , t s , and t sur are the temperature of the air, fuel, smoke (at furnace exit), and surroundings, respectively,°C; t mg is the average temperature of the molten glass at the entrance into the channel,°C; c mg is the specific heat capacity of the molten glass at t mg , kJ/(kg × K); L a and V a are the flow rate of the air and smoke for the actual air flow rate coefficient (a = 1.1), respectively, m 3 /m 3 gas; F i is the area of the ith surface of the furnace masonry, m 2 ; K i is the average coefficient of heat transfer through the ith surface of the masonry, W/(m 2 × K); t i int is the integral average i...