Electric furnace waste heat recovery method and apparatus

Claim 2

In an electric furnace that discharges a high temperature exhaust gas laden with dust, said furnace comprising electrode means having first cooling means associated therewith, a cover having conduit means for discharging the exhaust gas from the furnace and having second cooling means associated with said conduit means, means for circulating a first liquid coolant through said first and second cooling means for cooling said electrode means and said conduit means whereby to discharge said first coolant in a heated liquid state under atmospheric pressure; a first heat exchanger having internal tube means connected to said conduit means for receiving exhaust gas therefrom, said internal tube means being constructed so as to repel adhesion of dust present in said exhaust gas and so as to be easily cleanable if dust is deposited thereon, said first heat exchanger including means to circulate a second gaseous coolant in indirect heat exchange relationship with said internal tube means whereby to discharge from said first heat exchanger a stream of second gaseous coolant heated to a temperature higher than the boiling point of said first coolant; and a second heat exchanger connected to receive and to effect heat exchange between said first coolant and said second coolant whereby said first coolant is heated to a higher temperature.

Claim 3

An electric furnace according to claim 1 wherein said first heat exchanger is a shell-and-tube heat exchanger wherein the tube means have fins projecting from the external surface thereof.

Claim 4

An electric furnace according to claim 2 wherein said tube means of said first heat exchanger are internally unobstructed, straight and of constant internal size throughout their length.

Claim 5

An electric furnace according to claim 2 including fan means for circulating a stream of said second coolant through the shell side of said first heat exchanger.

Claim 6

An electric furnace according to claim 1 wherein said second heat exchanger comprises a shell-and-tube heat exchanger, and including means for circulating one of said coolants through the shell side thereof and means for circulating the other of said coolants through the tube side thereof.

Claim 7

An electric furnace according to claim 1 including a vessel for receiving said first coolant in the liquid state, under atmospheric pressure, after said first liquid has circulated through said first and second cooling means and pump means for pumping said first coolant from said vessel into said second heat exchanger.

Claim 8

An electric furnace according to claim 6 including a second vessel connected for receiving said first coolant from said first cooling means, second pump means for pumping said first coolant from said second vessel through said second cooling means and thence into said first vessel and means for controlling the rate of flow of the first coolant from said second vessel to said first vessel.

Claim 9

A process for recovering waste heat from an electric furnace that discharges a high-temperature exhaust gas having high dust loading, which comprises the steps of: in a primary heat recovery stage, flowing a relatively cool, heat-exchange liquid in indirect heat-exchange relationship with the high-temperature exhaust gas discharged from said furnace so that said heat-exchange liquid removes heat from the exhaust gas whereby to partially cool the exhaust gas and to effect primary heat recovery therefrom, and thereby heating said heat-exchange liquid to a temperature lower than the boiling point thereof under atmospheric pressure, and then discharging said heated heat-exchange liquid from said primary heat recovery stage into an atmospheric pressure zone; in a secondary heat recovery stage, flowing the partially cooled exhaust gas through tube means constructed to repel adhesion of dust and to permit easy removal of any dust deposited thereon and simultaneously passing a relatively cool heat-exchange gas along the opposite side of said tube means in indirect heat-exchange relationship with the exhaust gas so that said heat-exchange gas removes heat from the exhaust gas and is heated to a temperature higher than the boiling point of said heat-exchange liquid, and discharging said heated heat-exchange gas from said secondary heat recovery stage; and in a final heat recovery stage, flowing said heat-exchange liquid from said atmospheric pressure zone in heat-exchange relationship with said heat-exchange gas that was discharged from said secondary heat recovery stage, whereby to raise the temperature of said heat-exchange liquid.

Claim 10

A process for recovering waste heat from an electric furnace that discharges a high-temperature exhaust gas having high dust loading, which comprises the steps of: in a primary heat recovery stage, flowing a relatively cool, heat-exchange liquid in indirect heat-exchange relationship with the high-temperature exhaust gas discharged from said furnace so that said heat-exchange liquid removes heat from the exhaust gas whereby to partially cool the exhaust gas and to effect primary heat recovery therefrom, and thereby heating said heat-exchange liquid to a temperature lower than the boiling point thereof under atmospheric pressure, and then discharging said heated heat-exchange liquid from said primary heat recovery stage into an atmospheric pressure zone; in a secondary heat recovery stage, flowing the partially cooled exhaust gas through tube means constructed to repel adhesion of dust and to permit easy removal of any dust deposited thereon and simultaneously passing a relatively cool heat-exchange gas along the opposite side of said tube means in indirect heat-exchange relationship with the exhaust gas so that said heat-exchange gas removes heat from the exhaust gas and is heated to a temperature higher than the boiling point of said heat-exchange liquid, and discharging said heated heat-exchange gas from said secondary heat recovery stage; and in a final heat recovery stage, flowing said heat-exchange liquid from said atmospheric pressure zone in heat-exchange relationship with said heat-exchange gas that was discharged from said secondary heat recovery stage, whereby to raise the temperature of said heat-exchange liquid.