METHOD OF PRODUCING CEMENT CLINKER FROM A SOURCE OF CALCIUM SULFATE
A method of producing cement clinker from a source of calcium sulfate, includes calcining the source of calcium sulfate in the presence of a reducing agent in a first reactor to obtain calcium oxide and sulfur dioxide and withdrawing the calcium oxide from the first reactor, and subsequently adding silica, alumina and iron oxide to the calcium oxide to obtain a raw material mixture and calcining the raw material mixture in a second rector to obtain cement clinker.
1 . A method of producing cement clinker from a source of calcium sulfate, comprising
a first step of calcining the source of calcium sulfate in the presence of a reducing agent in a first reactor to obtain calcium oxide and sulfur dioxide and withdrawing the calcium oxide from the first reactor, and subsequently
a second step of adding silica, alumina and iron oxide containing materials to the calcium oxide to obtain a raw material mixture and calcining the raw material mixture in a second rector to obtain cement clinker.
2 . The method according to claim 1 , wherein the calcination of the first step is carried out at a temperature of 700-1300° C. and the calcination of the second step is carried out at a temperature of 1340-1450° C.
3 . The method according to claim 1 , wherein the source of calcium sulfate is gypsum, anhydrite, hemihydrate, waste calcium sulfate and/or phosphogypsum.
4 . The method according to claim 1 , wherein the source of calcium sulfate is introduced into the first reactor in the form of a powder.
5 . The method according to claim 1 , wherein the source of calcium sulfate is dried to a water content of <2 wt. -% before being introduced into the first reactor.
6 . The method according to claim 1 , wherein the first step is carried out in a reducing atmosphere.
7 . The method according to claim 1 , wherein a source of carbon in solid form, a metal powder, or hydrogen, is used as the reducing agent.
8 . The method according to claim 1 , wherein the first reactor is designed as a flash calciner, rotary calciner, fluidized bed reactor or shaft reactor.
9 . The method according to claim 1 , wherein the second reactor is designed as a rotary kiln.
10 . The method according to claim 1 , wherein the sulfur dioxide obtained in the first step is separated from the calcium oxide, before the calcium oxide is fed to the second step.
11 . The method according to claim 1 , wherein the calcium oxide coming from the first step is allowed to cool to ambient temperature and is stored before being used in the second step.
12 . The method according to claim 1 , wherein the calcium oxide is withdrawn from the first reactor at a first temperature and is introduced into the second rector at a second temperature that is <100° C. below the first temperature.
13 . The method according to claim 1 , wherein the silica, alumina and iron oxide containing materials comprise recycled or waste materials.
14 . The method according to claim 13 , wherein the recycled or waste materials are selected from any of the following materials: mineral waste materials from construction and demolition, recycled aggregates, recycled bricks, coal ashes, or steel slags.
15 . The method according to claim 2 , wherein the second step is carried out at higher temperature than the first step.
16 . The method according to claim 4 , wherein the powder has a maximum particle size of 300 pm measured by sieving.
17 . The method according to claim 6 , wherein the oxygen content is below 0.7 vol. -%.
18 . The method according to claim 7 , wherein the source of carbon is coal in powder form, or wherein the metal powder comprises calcium, aluminum, silicium, iron, or mixtures thereof.
19 . The method according to claim 14 , wherein the waste materials from construction and demolition comprise concrete demolition waste.