GB2375160A

GB2375160A - Furnace injection apparatus

Info

Publication number: GB2375160A
Application number: GB0111127A
Authority: GB
Inventors: Douglas Grant Dickie
Original assignee: CLYDE BERGEMANN Ltd
Current assignee: CLYDE BERGEMANN Ltd
Priority date: 2001-05-05
Filing date: 2001-05-05
Publication date: 2002-11-06
Anticipated expiration: 2021-05-05
Also published as: GB0111127D0; GB2375160B

Abstract

In an apparatus for the injection of a fine spray of a reactant gas into a combustion space, e.g. a furnace, a lance body 22, is retractably mounted so that it can project into the combustion space and comprises a plurality of nozzles 24, spaced along the length of the body. A system of conduits (28',30',32' Fig2) housed within the lance body is arranged to receive and conduct the cooling, reactant and atomisation fluids from external connections 28,30,32; the reactant and atomisation fluid section being easily removable from the lance body for cleaning and maintenance purposes.

Description

INJECTION APPARATUS The invention relates to lance-type injection apparatus for injection of chemical

reactants into a working space, particularly but not exclusively into a furnace.

, Industrial boilers such as in power stations provide space for the efficient combustion of coal and other fossil fuels. Particularly when operating at high temperature, pollutants such as sulphur oxides (SOx) and especially nitrogen oxides (NOx) are formed in the combustion space. For environmental reasons there is a strong desire to eliminate these pollutants before releasing the flue gases to the atmosphere. It is known that the introduction of chemical reducing agents directly into the combustion space can remove a significant proportion of these pollutants. Typically the reactant is a solution of urea or ammonia, although the invention is not limited to these examples, and a wide range of different reactants are known.

As explained for example in US 5342592, to treat the effluent efficiently (and without causing other problems such as corrosion of heat exchange tubing) a uniform and fine spray of reactant should be injected under controlled conditions at a very hot part of the combustion space (around 1000 C). In US 5342592 a lance-type injector is proposed which comprises effectively four concentric conduits extending through a side wall of the furnace and into the hot space. The outer two conduits form a cooling jacket, and provide for flow and return of cooling medium (such as water), which is necessary to keep the lance from destruction in the high temperature environment. The inner two conduits carry reactant solution and atomising air. The solution is pressurised and escapes into the combustion space via openings spaced at intervals along the lance. The atomising air is channelled to the openings so as to meet and impinge upon each jet of reactant solution from two sides as it emerges, thereby to ensure a desired fan-shaped plume of reactant droplets.

It is an object of the invention to provide an alternative form of lance-type injector for introducing such reactants into a combustion space. In the hostile environment in which it operates, including the properties of the reactants which may corrode and/or clog the nozzles, ease of maintenance of the lance is a priority.

The invention provides an apparatus for the injection of reactant into a combustion space, the apparatus comprising; a lance body, means for mounting the lance body so as to project into the combustion space and connections external to the combustion space for receiving fluids for cooling, reactant, and atomisation, the lance body comprising a plurality of nozzle arrangements spaced along its length and housing a system of conduits within the lance body arranged to receive said fluids from said external connections and to conduct said fluids separately along the length of the lance, each nozzle arrangement in use receiving and mixing reactant and atomisation fluids for the ejection of a fine spray of reactant, wherein the conduit for cooling fluid comprises the body of the lance, the conduits for reactant and atomisation fluid being separate from the lance body and running in parallel beside one another within the lance body and being connected with said nozzle arrangements inside the lance body at each nozzle location.

The conduits and nozzles may form an inner assembly removable from the lance body as a unit. The parallel arrangement of supply conduits facilitates construction, compared with complex co-axial structures provided in the prior art.

The nozzle arrangements may be self-contained, aiming through apertures provided at corresponding locations in the lance body. This provides for greater control and ease of servicing, compared with arrangements where the atomising nozzle is formed in part by an aperture in the lance body itself.

The nozzle arrangements may project into apertures in the lance body, beyond an inner wall of the lance body, the conduits and nozzle arrangements being displaceable into the lance body prior to retraction from the lance body in an axial direction.

The lance body may provide cover plates at at least some nozzle locations, the cover plates being removable for servicing of the nozzle arrangements in place within the , lance body.

The mounting arrangement may include carriage means whereby the lance can be retracted from the combustion space for maintenance without disturbing said external connections.

Means may be provided for retracting the lance tube automatically in the event of failure in the flow of cooling fluid.

These and other aspects of the invention will be apparent to the skilled reader from a consideration of the embodiments described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which : Fig 1 shows schematically in cross section a boiler installation including a lance-type reactor embodying the present invention ; Fig 2 is a view of the mounting and drive machinery for the lance, viewed from outside the boiler, towards the boiler along the lance access.

Fig 3 is a detailed cross section of the lance and nozzle arrangement in a second embodiment of the lance type reactor of Fig 1

Fig 4 is a detailed cross section of the lance and nozzle arrangement in a first embodiment of the lance-type reactor of Fig 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS I Fig 1 shows schematically the major components and operation of a utility-scale boiler incorporating a lance-type reactor in accordance with the present invention. The boiler comprises an enclosure 10 having burners 12 projecting through the wall of enclosure 10 at a lower part thereof, and an exhaust port 14 at an upper part. Heat exchange tubing 16 is provided between combustion zone 18 near the burners 12 and exhaust zone 20 near the exhaust port 14.

A lance-type reactor is provided between the heat exchange tubing 16 and the exhaust zone 20. The reactor comprises primarily a lance 22 having nozzles 24 spaced at regular intervals along it. A housing and drive box 26 is mounted outside the boiler, for supporting and retracting lance 22. Fluid connections 28,30 and 32 are provided for cooling fluid C, liquid reactant R and atomising fluid A, respectively.

In operation, fuel F is injected by burners 12 and ignited to generate heat and combustion products in combustion zone 18. Hot combustion gases 34 pass over the heat exchange tubing 16 to generate steam or perform some other useful function. As the gases approach the exhaust zone 20, a fine mist of reactant R is ejected from each nozzle 24, in a highly diffuse plume 36 etc. By virtue of the atomising character of the nozzles 24, a fine mist of droplets is formed which reacts with the combustion pollutants at high temperature, within a delay of 1 to 2 seconds. As explained in the introduction, heavier droplets would require a longer reaction time, and may fall on the interior of the boiler and the heat exchange tubing, promoting corrosion. Because the nozzles are spaced along the lance, the fine mist can be distributed evenly throughout the hot space.

Referring now to Fig 2, this is an end view inside the housing 26, in the direction shown by arrow II in Fig 1.

The position of the inner wall of lance 22, hidden in this view, is indicated in broken lines at 40. At the rear end of the lance a flange coupling 42 is provided, including

connections for a supply of fluids R, A and C. The entry points of fluid connections 28, , 30 and 32 are shown schematically at the bottom right of Fig 2. Corresponding connections 28'30'and 32'are provided on the flange coupling 42 at the rear of the lance. Along the chain-dotted lines labelled, A, R and C in the diagram, flexible hoses (not shown for clarity) are provided to complete the fluid connection 28-28' (C), 30-30' (R) and 32-32' (A), while permitting travel of the lance 22 in the actual direction.

Lance 22 is supported bodily on a carriage 44 which in turn is guided on an I-beam 46, mounted within housing 26 so as to support the weight of the lance both retracted and fully extended. A motor and gear box unit 48 is also mounted on the carriage, to extend and retract lance 22 by means of a rack 50 and pinion wheel 52.

Fig 3 shows in detail the interior of lance 22, in a cross section taken through one of the nozzles 24. In this embodiment, lance 22 comprises primarily a long tube 60, which extends from the flange connection 42 outside the boiler to a closing end cap (not shown) within the boiler space. The lance tube 60 is made of high temperature, corrosion-resistant steel alloy, suitable to withstand the high temperatures and corrosive atmosphere within the boiler space. Lance body 22 is retractable, as mentioned already, to permit replacement in case of damage and/or corrosion wear. At regularly spaced locations corresponding to the positions of nozzles 24, an inclined aperture 62 is formed in wall 60, nozzle head 64 resting within aperture 62 so as to have a clear aim into the boiler space. In this embodiment, the lance tube 60 also defines the conduit for cooling fluid C, in this case, air.

In a separate assembly, which can be retracted entirely from lance 22 for maintenance, conduits 66 and 68 are provided for liquid reagent R and atomising fluid A respectively. At spaced locations along their length, these conduits 66 and 68 are joined

together by the nozzle assemblies 24. Each nozzle provides ducting 70 for liquid reagent and 72 for atomising air. These fluids are led to a mixing chamber 74 within nozzle head 64. From the mixing chamber, the mixed fluids R and A are ejected in a fine mist, via a restricted opening 76.

As mentioned already, the entire assembly comprising conduits 66 and 68, and the , nozzle arrangements 24 can be retracted : firstly into the lance body 60, and then axially out of the rear of the lance 22, by decoupling the flange collection 42, and of course the respective hoses. To facilitate this action, the conduits 66,68 are not fixed to or braced against the inside of the lance body, but are supported only at their ends by the flange connection 42 and the end cap of the lance (not shown). Coupled with the facility to retract the lance completely on its carriage 44, any part of the lance 22 which may be subject to clogging, heat damage or corrosion can be withdrawn for servicing and/or replacement at an appropriate interval.

In operation, as a first priority, cooling fluid, in this case air, is pumped at moderate pressure into the lance body 60, where it flows along the body and emerges by degrees through the openings 62, surrounding each nozzle head 64. To permit differential expansion of the conduits 66,68 versus the lance wall 60, the apertures 62 may be slightly elongated in the direction of the lance access.

To eject the desired plumes 36 of the reactant mist, reagent fluid R and atomising fluid A are simultaneously pumped through conduits 66 and 68, mixing and being atomised at each nozzle head 64. Reactant fluid R can be any suitable fluid, probably in aqueous solution. For the removal of NOx pollutants, for example, fluid R will normally be a solution of urea or ammonia. Atomising fluid A will normally be simply air. In order to ensure uniform pressure and hence a uniform plume 36 at each nozzle 24, conduits 66 and 68 may be provided so as to reduce in diameter, from the near end to the far end of lance 22. Alternatively, or in addition, the ports between conduits 66 and 78 and the nozzle may be progressively less restricted, for nozzles nearer to the far end of lance 22.

The lance 22 is designed to reside more or less continuously in the combustion gases, and to be retracted only for servicing. A pressure-sensitive switch is provided to detect failure of the cooling fluid flow (other sensors may be provided for the same purpose), this triggering automatic retraction of the lance 22 to prevent damage when the cooling feature fails. Redundant multiple lances and/or cooling circuits can be provided to

ensure total availability of the anti-pollution function, if required. i The embodiments described provide a particularly compact, robust and servicing lance- type injector for removal of pollutants in high-temperature combustion spaces. Numerous variations from the constructions shown are of course possible, as will now be described.

Referring to Fig 4, a modification of the Fig 3 arrangement includes a removable cover piece 80 surrounding each nozzle head, in place of the small aperture 62 in the lance wall 60. This allows servicing of the nozzle arrangement 24 while lance 22 is retracted into housing 26 and the housing 26 is opened, without retracting the internal assembly from the lance tube.

The skilled reader will understand that a number of lances and/or a different number of nozzles may be provided in a practical example, and of course the layout and operation of the boiler components can vary according to known or new design principles.

The nozzles may be individually sized to create a tailored discharge profile along the length of the lance. The nozzles may be made adjustable for fine control, and/or can be exchanged to adjust the discharge profile, after the lance is installed.

It will be appreciated that the orientation of the nozzles shown in Figs 3 and 4 is downwards at an angle, by way of example only. Depending on the arrangement of the combustion space and the flow directions of the gases therein, a lance 22 may be oriented to direct the tombs 36 upwards, as shown in figure 1, or in any preferred direction.

In extreme environments, air cooling may be insufficient and/or more efficient cooling might allow the use of a cheaper alloy for the lance wall 60. Alternative embodiments are therefore envisaged, in which water cooling is provided, by means of a double wall arrangement. Whereas the cooling fluid C in the form of air is permitted to escape around each nozzle head into the combustion space, it will generally be necessary for

water to be channelled firstly out along the lance, and then back within the lance, to be , discharged or recycled outside the combustion space.

These and other modifications will be readily implemented by the skilled person based on the present disclosure. The invention is not intended to be limited by the examples discussed but rather by the terms of the appended claims.

Claims

CLAIMS 1. An apparatus for the injection of reactant into a combustion space; the apparatus comprising a lance body, means for mounting the lance body so as to project into the combustion space and connections external to the combustion space for receiving fluids

for cooling, reactant, and atomisation ; the lance body comprising a plurality of nozzle , arrangements spaced along its length and housing a system of conduits within the lance body arranged to receive said fluids from said external connections and to conduct said fluids separately along the length of the lance, each nozzle arrangement in use receiving and mixing reactant and atomisation fluids for the ejection of a fine spray of reactant, wherein the conduit for cooling fluid comprises the body of the lance, the conduits for reactant and atomisation fluid being separate from the lance body and running in parallel beside one another within the lance body and being connected with said nozzle arrangements inside the lance body at each nozzle location.
2. An apparatus as claimed in claim 1, wherein said conduits and nozzles form an inner assembly removable from the lance body as a unit.
3. An apparatus as claimed in claims 1 or 2, wherein the nozzle arrangements are self-contained, aiming through apertures provided at corresponding locations in the lance body.
4. An apparatus as claimed in claim 1, 2 or 3, wherein the nozzle arrangements project into apertures in the lance body, beyond an inner wall of the lance body, the conduits and nozzle arrangements being displaceable into the lance body prior to retraction from the lance body in an axial direction.
5. An apparatus as claimed in any preceding claim, wherein the lance body provides cover plates at at least some nozzle locations, the cover plates being removable for servicing of the nozzle arrangements in place within the lance body.

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6. An apparatus as claimed in any preceding claim, wherein the mounting arrangement includes carriage means whereby the lance can be retracted from the combustion space for maintenance without disturbing said external connections.
7. An apparatus as claimed in claim 6, wherein means is provided for retracting

the lance tube automatically in the event of failure in the flow of cooling fluid.

I
8. An apparatus for the injection of reactant into a combustion space substantially as hereinbefore described with reference to figures 1,2 and 3 of the drawings.
9. An apparatus for the injection of reactant into a combustion space substantially as hereinbefore described with reference to figures 1,2 and 4 drawings.