Method for operating a batch furnace comprising the preheating of a fluid upstream of the furnace

Patent metadata

Field	Value
Publication number	US-11378338-B2
Application number	US-201716316235-A
Country	US
Kind code	B2
Filing date	Jun 29, 2017
Priority date	Jul 8, 2016
Publication date	Jul 5, 2022
Grant date	Jul 5, 2022

Abstract

Furnace operation includes consecutive cycles of a heating step, a stopping step and a restarting step. The fuel and/or the oxidizing agent is preheated upstream of the furnace by indirect exchange with the discharged fumes through a medium passing through a chamber. A first wall separates the fumes from the medium in the chamber. The fuel and/or oxidizing agent is separated from the medium in the chamber by a second wall. During restarting, the medium's flow rate Dm is regulated to limit the heating rate of the first wall until it reaches the operational temperature at an end thereof.

First claim

What is claimed is:

1. A process for operating a furnace, said process comprising repeating a cycle of a heating step followed by a shutdown step and a restarting step, said heating step comprising the steps of:
supplying a fuel and an oxidant to the furnace whereby the furnace is heated by combustion of the supplied fuel with the oxidant with generation of heat and flue gases;
discharging the flue gases from the furnace through a duct; and
preheating a fluid chosen from the fuel and the oxidant upstream of the furnace by:
introducing a flow rate Dm >0 of a liquid or gaseous medium into a chamber and heating said medium by heat exchange with the flue gases in the duct across a first wall which separates the medium in the chamber from the flue gases in the duct with a heated medium being obtained, and
introducing a flow rate Df >0 of the fluid to be preheated into at least one line so as to preheat the fluid by heat exchange with the heated medium in the chamber across a second wall which separates the fluid in the at least one line from the heated medium in the chamber and which has a temperature referred to as operational temperature, wherein:

during the shutdown step, each of the supply of the fuel to the furnace, the supply of the oxidant to the furnace, the combustion of the fuel with the oxidant in the furnace, and the discharge of flue gases from the furnace through the duct are interrupted;
during the shutdown step, the flow rate Dm of the medium in the chamber does not exceed 50% of the flow rate Dm during the heating step;
during the restarting step, each of the supply of the fuel to the furnace, the supply of the oxidant to the furnace, the combustion of the fuel with the oxidant in the furnace, and the discharge of flue gases from the furnace through the duct are restarted;
during the restarting step, a flow rate Dm of the medium is introduced into the chamber which is greater than the flow rate Dm during the shutdown step; and
during the restarting step, the flow rate Dm is regulated so as to limit the rate of heating of the first wall until the first wall reaches the operational temperature at the end of the restarting step.

2. The process of claim 1 , wherein, during the shutdown step, the flow rate Dm=0.

3. The process of claim 1 , wherein, during the restarting step, the flow rate Dm rises above the flow rate Dm during the heating step in order to then return to the flow rate Dm of the heating step at the end of the restarting step.

4. The process of claim 1 , wherein, during the restarting step, the flow rate Dm does not exceed the flow rate Dm during the heating step.

5. The process of claim 1 , wherein the flow rate Dm during the restarting step is regulated so that during the restarting step the first wall heats at a heating rate V T↑ which is less than or equal to a predetermined upper limit V T↑max .

6. The process of claim 1 , wherein, during the restarting step, the flow rate Dm changes according to a predetermined function.

7. The process of claim 5 , wherein, during the restarting step:
a temperature of the first wall is detected; and
the flow rate Dm is regulated as a function of the heating rate V T↑ determined from the detected temperature.

8. The process of claim 1 , wherein the heating step is a step of the treatment of a feedstock in the furnace.

9. The process of claim 8 , wherein, during the shutdown step, the heated feedstock is discharged from the furnace and a feedstock to be heated is introduced into the furnace.

10. The process of claim 1 , wherein the medium is a gaseous medium chosen from air, nitrogen, CO2 or steam.

11. The process of claim 1 , wherein the fluid to be preheated is an oxidant with an oxygen content between 50 vol % and 100 vol %.

12. The process of claim 1 , wherein oxidant and fuel are preheated during the heating step.

13. The process of claim 1 , wherein the furnace is chosen from rotary furnaces for smelting of cast iron, rotary furnaces for smelting of nonferrous metals, tilting furnaces for smelting of nonferrous metals, rotary or tilting furnaces for smelting of enamels, and furnaces for smelting of metals of electric arc furnace type.

14. The process of claim 1 , wherein the fluid to be preheated is the fuel and, during the restarting step, the fuel is split into two portions: a first portion and a second portion, wherein:
the first portion is supplied directly to the furnace without passing through the at least one line; and
the second portion is supplied to the furnace after having passed through the at least one line.

15. The process of claim 14 , wherein a ratio, between, the second portion of the fluid and the sum of the first portion of the fluid and the second portion of the fluid, increases during the starting step.

16. The process of claim 1 , wherein the fluid to be preheated is the oxidant and, during the restarting step, the oxidant is split into two portions: a first portion and a second portion, wherein:
the first portion is supplied directly to the furnace without passing through the at least one line; and
the second portion is supplied to the furnace after having passed through the at least one line.

Assignees

• Air Liquide

Inventors

• Jarry Luc
• Van Kampen Peter

Classifications

• F27D17/13

  using regenerative heat exchangers · CPC title

• F27D17/10

  Arrangements for using waste heat · CPC title

• F23L15/045 Primary

  using intermediate heat-transfer fluids · CPC title

• F27B7/34

  Arrangements of heating devices · CPC title

• F27B3/20

  Arrangements of heating devices · CPC title