Furnace operation method

1 . A method for operating a furnace, comprising:

a. combusting fuel with oxidant, thereby generating thermal energy and fumes,

b. heating the furnace with a first part of the thermal energy generated in step a,

c. evacuating the generated fumes from the furnace at a temperature of at least 900° C., the evacuated fumes containing a second part of the thermal energy generated in step a,

d. using the second part of the thermal energy generated in step a:

i. for heating the oxidant, as fluid to be heated, by direct or indirect heat exchange with the evacuated fumes, as heat-bearing fluid, before the heated oxidant is used to combust the fuel in step a, and

ii. as a heat source for cracking ammonia in a cracker into a mixture comprising hydrogen, nitrogen and un-cracked ammonia,

wherein the ammonia is cracked without the use of catalyst, and

wherein the ammonia is heated to a temperature of 1000° C.;

whereby:

during direct heat exchange, the heat-bearing fluid and fluid to be heated are physically separated from one another by a fluid-impermeable heat-conducting wall across which heat is transferred from the heat-bearing fluid to the fluid to be heated, while preventing mixing between the heat-bearing fluid and the fluid to be heated; and

during indirect heat exchange:

an intermediate heat-transfer fluid is used, the heat-bearing fluid and the intermediate fluid are physically separated from one another by a first fluid-impermeable heat-conducting wall across which heat is transferred from the heat-bearing fluid to the intermediate fluid, while preventing mixing between the heat-bearing fluid and the intermediate fluid, so as to obtain a heated intermediate fluid, and

the heated intermediate fluid and the fluid to be heated are separated from one another by a second fluid-impermeable heat-conducting wall across which heat is transferred from the intermediate fluid to the fluid to be heated, while preventing mixing between the heated intermediate fluid and the fluid to be heated; and

whereby, in step a, at least part of the mixture produced in step d-ii is combusted as fuel in step a with at least part of the heated oxidant produced in step d-i.

2 . The method according to claim 1 , whereby a NOx-reducing agent is added to the evacuated fumes before step d and/or after step d and/or between step d-i and d-ii.

3 . The method according to claim 2 , whereby ammonia is used as NOx reducing agent.

4 . The method according to claim 1 , whereby, in step d-i, the oxidant is heated by indirect heat exchange with the evacuated fumes and whereby, in step d-ii, the ammonia is heated by direct heat exchange with the evacuated fumes upstream of and/or in the cracker.

5 . The method according to claim 4 :

a. whereby a first portion of the evacuated fumes is used to heat the oxidant in step d-i and a second portion of the evacuated fumes is used to heat the ammonia in step d-ii, or

b. whereby, in step d-ii, the ammonia is heated by direct heat exchange with the evacuated fumes previously used in step d-i for heating the oxidant, or

c. whereby, in step d-i, the oxidant is heated by indirect heat exchange with the evacuated fumes previously used in step d-ii for heating the ammonia.

6 . The method according to claim 1 , whereby the oxidant and the ammonia are heated by direct heat exchange with the evacuated fumes in steps d-i, respectively d-ii.

7 . The method according to claim 6 :

a. whereby, a first portion of the evacuated fumes is used to heat the oxidant in step d-i and a second portion of the evacuated fumes is used to heat the ammonia in step d-ii, or

b. whereby, in step d-ii, the ammonia is heated by direct heat exchange with the evacuated fumes previously used in step d-i for heating the oxidant, or

c. whereby, in step d-i, the oxidant is heated by direct heat exchange with the evacuated fumes previously used in step d-ii for heating the ammonia.

8 . The method according to claim 1 , whereby the oxidant and the ammonia are heated by indirect heat exchange with the evacuated fumes in steps d-i, d-ii respectively.

9 . The method according to claim 8 :

a. whereby, a first portion of the evacuated fumes is used to heat the oxidant in step d-i and a second portion of the evacuated fumes is used to heat the ammonia in step d-ii, or

b. whereby, in step d, the second part of the thermal energy generated in step a is used to heat a first and a second intermediate fluid, the first intermediate fluid is used for heating the oxidant in step d-i and the second intermediate fluid is used in step d-ii for heating the ammonia upstream of and/or in the cracker, or

c. whereby the evacuated fumes are used to heat an intermediate fluid and whereby the heated intermediate fluid is used for heating the oxidant in step d-i and for heating the ammonia upstream of and/or in the cracker.

10 . The method according to claim 9 , whereby, in step d, the second part of the thermal energy generated in step a is used to heat a first and a second intermediate fluid, the first intermediate fluid is used for heating the oxidant in step d-i and the second intermediate fluid is used in step d-ii for heating the ammonia upstream of and/or in the cracker and:

a. whereby the second intermediate fluid is heated by heat exchange with the evacuated fumes previously used for heating the first intermediate fluid, or

b. whereby the first intermediate fluid is heated by heat exchange with the evacuated fumes previously used for heating the second intermediate fluid.

11 . The method according to claim 9 , whereby the evacuated fumes are used to heat an intermediate fluid and whereby the heated intermediate fluid is used for heating the oxidant in step d-i and for heating the ammonia upstream of and/or in the cracker and

a. whereby a first portion of the heated intermediate fluid is used for heating the oxidant in step d-i and whereby a second portion of the intermediate fluid is used in step d-ii for heating the ammonia upstream of and/or in the cracker, or

b. whereby, in step d-ii, the ammonia is heated by direct heat exchange with the heated intermediate fluid previously used in step d-i for heating the oxidant, or

c. whereby, in step d-i, the oxidant is heated by direct heat exchange with the heated intermediate fluid previously used in step d-ii for heating the ammonia.

12 . The method according to claim 1 , whereby the oxidant and the ammonia are heated respectively in step d-i and step d-ii in a combined heat-exchanger/cracker.

13 . The method according to claim 1 , whereby the furnace is a glass furnace selected from the group consisting of glass-melting furnaces, glass-refining furnaces and glass-melting-and-refining furnaces.