Combustion system and combustion method

Abstract

The combustion system includes a boiler and a flue gas treatment system downstream of the boiler. The flue gas treatment system includes a desulphurization unit, a carbonator and a calciner defining a carbonator/calciner loop. The flue gas from the desulphurization unit is fed into the carbonator. No air pre-heaters, for pre-heating combustion oxidizer to be supplied into the boiler using heat of flue gas, are provided at the boiler and between the boiler and the carbonator.

Claims

1. A combustion system comprising a boiler and a flue gas treatment system downstream of the boiler, the flue gas treatment system comprising: a desulphurization unit; and a carbonator and a calciner defining a carbonator/calciner loop, the flue gas from the desulphurization unit being fed into the carbonator; wherein no air pre-heaters, for pre-heating combustion oxidizer to be supplied into the boiler using heat of flue gas, are provided at the boiler and between the boiler and the carbonator; wherein the flue gas discharged from the boiler has a temperature above 350 C.; and wherein the gas treatment system includes a dust removal unit upstream of the desulphurization unit.

2. The combustion system of claim 1, wherein the desulphurization unit includes at least a sorbent injector and at least a filter, the at least a sorbent injector for supplying sorbent into the flue gas for reaction with at least gaseous sulphur components contained in the flue gas to form at least solid sulphur components, and the least a filter for catching the at least solid sulphur components.

3. The combustion system of claim 1, further comprising a heat exchanger is provided between the desulphurization unit and the carbonator, to heat the flue gas supplied into the carbonator.

4. A method for operating a combustion system having a boiler and a flue gas treatment system downstream of the boiler, the method comprising: combusting a fuel with an oxidizer generating flue gas; removing sulphur components from the flue gas; and supplying the flue gas deprived of the sulphur components into a carbonator of a carbonator/calciner loop, wherein no pre-heating of the oxidizer to be supplied into the boiler, using heat of the flue gas, at the boiler and between the boiler and the carbonator is carried out, wherein the flue gas discharged from the boiler has a temperature above 350 C.; and further comprising removing dust from the flue gas before removing the sulphur components.

5. The method of claim 4, wherein removing sulphur components comprises: injecting a sorbent into the flue gas, for the sorbent to react with gaseous sulphur components contained in the flue gas to form at least solid sulphur components; and catching the solid sulphur components.

6. The method of claim 5, wherein the solid sulphur components are removed by passing the flue gas through at least a filter.

7. The method of claim 4, wherein the flue gas is heated after removing sulphur components therefrom and before supplying the flue gas into the carbonator.

8. The method of claim 4, wherein the flue gas discharged from the boiler has a temperature above 380 C.

9. The method of claim 4, wherein the temperature of the flue gas into which the sorbent is injected and that is passed through at least a filter is above 350 C.

10. The method of claim 9, wherein the temperature of the flue gas into which the sorbent is injected and that is passed through at least a filter is above 380 C.

11. The method of claim 4, further comprising removing acidic components from the flue gas together with the sulphur components.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further characteristics and advantages will be more apparent from the description of a preferred but non-exclusive embodiment of the system and method, illustrated by way of non-limiting example in the accompanying drawings, in which:

(2) FIG. 1 shows a boiler and a flue gas treatment system according to the prior art;

(3) FIG. 2 shows a boiler and a flue gas treatment system in an embodiment of the invention.

DETAILED DESCRIPTION

(4) With reference to FIG. 2, the combustion system 20 comprises a boiler 21 and a flue gas treatment system 22 connected downstream of the boiler 21 via a flue gas duct 35.

(5) The boiler is used for generating steam, for example for a power plant.

(6) The flue gas treatment system 22 comprises a dust removal unit 25 (but this is not mandatory) and a desulphurization unit 26; preferably, the dust removal unit is provided upstream of the desulphurization unit 26.

(7) The desulphurization unit 26 preferably includes at least a sorbent injector 27 and at least a filter 28, e.g. a fabric filter.

(8) The sorbent injector 27 supplies a sorbent such as Ca(OH).sub.2 into the flue gas; the sorbent reacts with gaseous sulphur components contained in the flue gas to form solid sulphur components that are captured in the filter 28.

(9) Downstream of the desulphurization unit 26 a heat exchanger 30 is provided; the heat exchanger 30 is provided between the desulphurization unit 26 and the carbonator of the carbonator/calciner loop 31, to heat the flue gas supplied into the carbonator. According to the particular design conditions, the heat exchanger 30 could be excluded, i.e. the heat exchanger 30 is optional and it is used only if needed.

(10) Downstream of the desulphurization unit 26 and heat exchanger 30 the carbonator calciner loop 31 is provided. In particular, as known, the flue gas is supplied into the carbonator.

(11) In contrast to what is shown in the prior art, no air pre-heaters are provided using heat from the flue gas for pre-heating of the combustion air to be supplied into the boiler 21, neither at the boiler 21 nor between the boiler 21 and the carbonator of the carbonator/calciner loop 31.

(12) The operation of the combustion system 20 is apparent from what is described and illustrated and is substantially the following.

(13) The boiler 21 is supplied with fuel 33 and oxidizer 34 such as air for burning the fuel to generate heat, which is used to generate steam (that is for example directed to a steam turbine), and flue gas.

(14) The flue gas is discharged from the boiler 21 at a relatively high temperature, for example higher than 350 C. and preferably 380 C. as the flue gas is no longer used to heat the combustion air supplied to the boiler 21. The flue gas maintains the high temperature in the duct 35.

(15) The flue gas is thus directed through the optional dust removal unit 25 where dust is removed and then flue gas is directed to the desulphurization unit 26 where a sorbent such as Ca(OH).sub.2 is injected into the flue gas to remove sulphur components and possibly other acidic components such as HCl.

(16) For example the reactions are:
Ca(OH).sub.2+SO.sub.2<-->CaSO.sub.3+H.sub.2O
Ca(OH).sub.2+SO.sub.2+O.sub.2<-->CaSO.sub.4+H.sub.2O
Ca(OH).sub.2+2HCl<-->CaCl.sub.2+2H.sub.2O

(17) The flue gas discharged from the desulphurization unit 26 has still a relatively high temperature, because only a low temperature decrease occurs when passing through the dust removal unit 25 and the desulphurization unit 26.

(18) The flue gas is then supplied into the carbonator. The carbonator has an operating temperature of about 550-650 C. and therefore the flue gas might be passed through the heat exchanger 30 where it is heated before being supplied into the carbonator; The required heating at the heat exchanger 30 is now however less than in the prior art.

(19) According to the particular design, the heat exchanger 30 could also be avoided, if the temperature of the flue gas from the desulphurization unit 26 fits with the required temperature at the carbonator (i.e. is the same as or is close enough to the temperature at the carbonator).

(20) The flue gas is finally supplied into the carbonator of the carbonator/calciner loop 31.

(21) The present disclosure also refers to a method for operating a combustion system comprising a boiler 21 and a flue gas treatment system 22 downstream of the boiler 21.

(22) The method comprises combusting a fuel with an oxidiser such as air generating flue gas, removing sulphur and possibly other acidic components from the flue gas, supplying the flue gas deprived of the sulphur components into a carbonator of a carbonator/calciner loop 31.

(23) Advantageously, the oxidizer to be supplied into the boiler, is not pre-heated using heat from the flue, gas, at the boiler 21 and between the boiler 21 and the carbonator.

(24) In addition and preferably, the flue gas to be supplied into the desulphurisation unit is not cooled before entering the carbonator.

(25) Preferably removing sulphur and possibly other acidic components comprises injecting a sorbent into the flue gas, for the sorbent to react with gaseous sulphur and acidic components contained in the flue gas to form solid sulphur and chloride components, and then removing these components for example by passing the flue gas through at least a filter.

(26) In addition, after removing sulphur and possibly other acidic components from the flue gas and before supplying the flue gas into the carbonator, the flue gas is preferably heated. In preferred embodiments, the flue gas discharged from the boiler 21 has a temperature above 350 C. and preferably above 380 C.

(27) Naturally the features described may be independently provided from one another.

(28) In practice the materials used and the dimensions can be chosen at will according to requirements and to the state of the art.