Oxy-calcination process

Abstract

Method and installation for calcining cement raw meal in a calciner whereby fuel and a calciner oxidant having an oxygen content of at least 30% vol are introduced into the calciner so as to generate either an oxidant-lean zone or a fuel-lean zone in the calciner located between the lowermost fuel inlet level and the lowermost oxidant inlet level of the calciner, between 50% and 100% by weight of the raw meal being supplied to the calciner upstream of and/or within the oxidant-lean, respectively the fuel-lean zone.

Claims

1. A calcination installation for calcining cement raw meal, the installation comprising a calciner having a total calciner height and extending between a bottom end and a top end in a longitudinal direction, the calciner comprising: a lowermost oxidant inlet level at which one or more first oxidant inlets are located, and optionally one or more second oxidant inlet levels located above the lowermost oxidant inlet level in the longitudinal direction and at which one or more second oxidant inlets are located, said first oxidant inlets and, if present, said second oxidant inlets being connected to a source of calciner oxidant having an oxygen content of at least 30% vol; a lowermost fuel inlet level at which one or more first fuel inlets are located; a flue gas outlet located at the top end of the calciner; a flue-gas recycle inlet located at the bottom end of the calciner; and one or more raw meal inlets, wherein: the lowermost oxidant inlet level is located above the lowermost fuel inlet level at an oxygen-lean zone distance Do>0 from said lowermost oxidant inlet in the longitudinal direction, at least one raw meal inlet being located below or at the lowermost oxidant inlet level in the longitudinal direction,; at least one raw meal inlet is located below or at the lowermost oxidant inlet level in the longitudinal direction; and the oxygen-lean zone distance Do is between 1/10and 4/10of the total calciner height.

2. The calcination installation of claim 1, further comprising a raw meal preheater connected to the flue gas outlet and to the one or more raw meal inlets of the calciner.

3. The calcination installation of claim 2, further comprising a flue gas purification installation connected to the flue gas outlet of the calciner, said flue gas purification installation being adapted for removing components other than CO.sub.2 from flue gas evacuated from the calciner via the flue gas outlet.

4. A cement clinker production unit comprising a calcination installation of claim 1 and a clinkerisation kiln, the clinkerization kiln being connected to the calcination installation so that meal calcined in the calciner is transferred to the clinkerization kiln.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The present invention and its advantages will be better understood in the light of the examples below, reference being made to FIGS. 1 and 2, whereby: FIG. 1 is a partial schematic representation of an installation suitable for use in the calcination method according to option 1 of the present invention, and FIG. 2 is a partial schematic representation of an installation suitable for use in the calcination method according to option 2 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(2) FIG. 1 shows a calciner 10 extending, in its vertical longitudinal direction, between a bottom end 11 and a top end 12, the calciner having a total height H.

(3) In the illustrated example, all of the fuel 13 is introduced into a riser duct 19 upstream of bottom end 11. In the present case, the solid fuel 13 is petcoke, but a combination of different fuels, including waste fuels and/or fossil fuels, may be introduced, for example at different locations of the calciner 10.

(4) The illustrated calciner 10 thus has only a single fuel inlet level, i.e. the lowermost inlet level L13, which coincides with the (level of the) bottom end 11 of the calciner, the riser duct connection to the bottom end 11 of the calciner acting as the single fuel inlet L13 into the calciner 10.

(5) All of the calciner oxidant 16 is introduced into the calciner 10 at level L16 via multiple oxidant inlets evenly distributed around the circumference of the calciner 10.

(6) The calciner oxidant 16 has an oxygen content of 99% vol. All of the calciner oxidant 16 is injected into the calciner 10 at level L16, level L16 thus being the sole and lowermost oxidant inlet level of the calciner, the oxidant inlets at level L16 being first oxidant inlets as defined above. Via said first oxidant inlets, the calciner oxidant is introduced into the calciner 10 in an amount sufficient to ensure complete combustion of the overall amount of fuel, while minimizing any excess oxygen in the calciner flue gas.

(7) Do is the oxygen-lean zone distance between the upstream lowermost fuel inlet level L13 and the downstream lowermost oxidant inlet level L16. The zone in the calciner 10 between the lowermost fuel inlet level L13 and lowermost oxidant inlet level L16, i.e. between bottom end 11 and level L16, is an oxygen-lean zone in which little or no fuel combustion takes place.

(8) A first portion 14 of (preheated) raw meal is injected into riser duct 19 upstream of calciner 10. This first portion 14 of the raw meal is thus introduced into the calciner 10 via its bottom end 11 where it enters said oxygen-lean zone. The remainder 15 of the (preheated) raw meal is injected into the oxygen-lean zone of calciner 10 via a raw meal inlet positioned at level L15 downstream of the lowermost fuel inlet level L13 and upstream of the lowermost oxygen inlet level L16.

(9) The raw meal 14, 15 introduced into the calciner 10 is entrained towards the top end 12 of the calciner 10 by an upward gas flow. During its upward passage through the calciner 10, the raw meal is at least partially, and in fact for at least 92%, calcined under the influence of heat generated by the burning of the fuel 13 with the calciner oxidant 16 and by any heat introduced into the calciner 10 by means of recycle flue gas. In the present context partially and totally calcined cement meal leaving the calciner are indiscriminately referred to as “calcined meal”. The calcined meal is evacuated from the calciner 10 via its top end 12 together with the calciner flue gas.

(10) The upstream gas stream which entrains the raw meal comprises fumes generated by the burning of the fuel 13 and decarbonation gas (CO.sub.2) generated by the decarbonation of the raw meal 14, 15. As will be explained hereinbelow, the upstream gas stream further comprises recycle flue gas.

(11) From the top end 12 of the calciner 10, the calciner flue gas and the calcined meal are transported to a first cyclone, separation cyclone 20, in which the calcined meal 21 is separated from the calciner flue gas.

(12) From separation cyclone 20, the separated calcined meal 21 is typically transported to a rotary clinkerization kiln (not represented) for the production of clinker. In the case of partial oxy-firing, combustion takes place in the rotary kiln with an oxidant having an oxygen content of less than 30% vol. From separation cyclone 20, the separated calciner flue gas is introduced into raw meal preheater tower 30 which comprises three further cyclones 31, 32, 33 through which the separated calciner flue gas flows in succession. Raw meal 40 to be preheated is introduced in the gas outlet of middle cyclone 32 via inlet 34 from where it is entrained by the gas flow into top cyclone 33. From top cyclone 33, the partially preheated raw meal is introduced into the gas outlet of bottom cyclone 31 (of the preheater tower 30) via inlet 35 from where it is entrained to middle cyclone 32. From middle cyclone 32, the raw meal is introduced into the gas outlet of separation cyclone 20 via inlet 36 from where it is entrained to bottom cyclone 31 of tower 30, whereafter the preheated raw meal is sent to meal splitter 50 before being introduced into calciner 10 as described above, i.e. indirectly via riser duct 19 and directly into calciner 10 at level L15.

(13) Extractor fan 60 extracts the calciner flue gas from top cyclone 33. Downstream of extractor fan 60 the calciner flue gas is split into two streams, a first stream 70, which is removed from the system and sent for downstream flue gas processing, and a second stream 80 of recycle flue gas which is recycled and introduced into calciner 10 via riser duct 19 and bottom end 11, as part of the upward gas flow in the calciner. If appropriate, the recycle flue gas 80 can be preheated before being reintroduced into calciner 10 (not illustrated). In the given example, the recycle flue gas 80 was introduced into the calciner at a temperature of 800 to 900° C.

(14) As mentioned above, the cement production installation may comprise a second raw meal preheater (not shown), which is, for example, fed with the flue gas of the rotary kiln.

(15) FIG. 2 shows an installation similar to the one shown in FIG. 1, but in which cement raw meal is calcined using the method of calcining cement raw meal according to the second option of the invention.

(16) In the illustrated example, all of the calciner oxidant 16′ is introduced into the riser duct 19 upstream of bottom end 11. Calciner 10 thus has only a single oxidant inlet level, i.e. the lowermost inlet oxidant level L16′, which coincides with the bottom end 11 of the calciner 10, the riser duct connection to the bottom end 11 of the calciner acting as the single oxidant inlet into the calciner 10.

(17) All of the fuel 13′ is introduced into the calciner 10 at level L13′ via a single fuel inlet or via multiple fuel inlets evenly distributed around the circumference of the calciner 10. Level L13′ is thus the sole and lowermost fuel inlet level of the calciner.

(18) Df is the fuel-lean zone distance between the upstream lowermost oxidant inlet level L16′ and the downstream lowermost fuel inlet level L13′, i.e. between the bottom end 11 and the lowermost fuel inlet level L13′. The zone in the calciner 10 between the bottom end 11 of the calciner 10 and level L13′ is a fuel-lean zone in which no fuel combustion takes place.

(19) Again, a first portion 14 of (preheated) raw meal is injected into riser duct 19 upstream of calciner 10. This first portion 14 of the raw meal is thus introduced into the calciner 10 via its bottom end 11 where it enters said fuel-lean zone. The remainder 15 of the (preheated) raw meal is injected into the oxygen-lean zone of calciner 10 via a raw meal inlet positioned at level L15 downstream of the lowermost oxidant inlet level L16′ and upstream of the lowermost fuel inlet level L13′.

(20) Apart from the above, the process and installation features are analogous to those of the previous example. Both options of the method according to the invention enable operation of the calciner 10 without any deterioration of the process due to material build-ups inside said calciner 10 while maintaining a high level of calcination. When, however, under otherwise similar process conditions, fuel, calciner oxidant and raw meal were introduced into calciner 10 with a configuration of the meal, fuel and calciner oxidant inlets and injection ratios known from the state of the art and not corresponding to a configuration according to the present invention, the process efficiency started to deteriorate within a few hours of operation due to increasing levels of material build-up in the calciner 10.

(21) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(22) The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

(23) “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.

(24) “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(25) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(26) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(27) All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.