WO1997001732A1 - Arrangement with an infeed grate in an incineration plant, especially a waste-incineration plant, and method of using said arrangement - Google Patents

Arrangement with an infeed grate in an incineration plant, especially a waste-incineration plant, and method of using said arrangement Download PDF

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Publication number
WO1997001732A1
WO1997001732A1 PCT/DK1996/000287 DK9600287W WO9701732A1 WO 1997001732 A1 WO1997001732 A1 WO 1997001732A1 DK 9600287 W DK9600287 W DK 9600287W WO 9701732 A1 WO9701732 A1 WO 9701732A1
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WO
WIPO (PCT)
Prior art keywords
grate
fuel
waste
weight
travelling
Prior art date
Application number
PCT/DK1996/000287
Other languages
French (fr)
Inventor
Siegfried Binner
Rasmus Stig Jensen
Original Assignee
Vølund Ecology Systems A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Vølund Ecology Systems A/S filed Critical Vølund Ecology Systems A/S
Priority to AU62990/96A priority Critical patent/AU6299096A/en
Publication of WO1997001732A1 publication Critical patent/WO1997001732A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N5/00—Systems for controlling combustion
    • F23N5/18—Systems for controlling combustion using detectors sensitive to rate of flow of air or fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
    • F23G5/002—Incineration of waste; Incinerator constructions; Details, accessories or control therefor characterised by their grates
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G5/00—Incineration of waste; Incinerator constructions; Details, accessories or control therefor
    • F23G5/50—Control or safety arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G2203/00—Furnace arrangements
    • F23G2203/101—Furnace arrangements with stepped or inclined grate
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G2900/00—Special features of, or arrangements for incinerators
    • F23G2900/55—Controlling; Monitoring or measuring
    • F23G2900/55007—Sensors arranged in waste loading zone, e.g. feed hopper level
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23G—CREMATION FURNACES; CONSUMING WASTE PRODUCTS BY COMBUSTION
    • F23G2900/00—Special features of, or arrangements for incinerators
    • F23G2900/55—Controlling; Monitoring or measuring
    • F23G2900/55009—Controlling stoker grate speed or vibrations for waste movement
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N2225/00—Measuring

Definitions

  • the present invention relates to an arrangement with a grate in an incineration plant, especially a waste-in ⁇ cineration plant, in which at least one grate is used for conveying fuel, especially waste, from a fuel supply to a combustion space, especially for plants in which at least one grate is used for conveying fuel through the combustion space and further to the slag discharge, said grate or grates being of the travelling-grate type with at least one movable grate part.
  • waste having been weighed is transferred to an unloading silo.
  • the waste is taken up from the unloading silo, normally by using a conveyor belt or a crane, the waste being weighed at the same time.
  • This weight measurement is transferred to the superior moni ⁇ toring system, making it possible to monitor the quantity of waste being incinerated in each incineration line.
  • the waste is delivered to the incineration plant as such through a filling hopper, after which it falls down into a fuel chute or shaft (waste chute or shaft) constituting a buffer store.
  • An infeed grate in the form of a travel- ling grate is situated in the bottom of the fuel chute or shaft and adapted to remove the waste from the bottom of the fuel chute or shaft.
  • the infeed grate will be succeeded by at least one grate in a combustion cham ⁇ ber, in which the waste is incinerated while air for combustion is supplied, partly in the form of primary air from below through the grate, partly in the form of secondary air to the combustion chamber.
  • the calorific value is normally low compared to other types of fuel, and the burning-out time may differ greatly for the individual components of the waste.
  • the lower calorific value i.e. the net contribution of energy per kg fuel, i.e. including losses due to heating-up and evaporation of water content, can typically have a value of 8,000 kJ/kg; this ⁇ hould be compared to the calorific value of plastic in the form of polyethylene of up to 44,800 kJ/kg and coal of up to 29,300 kJ/kg. Because of the water content and the burning-out time of the waste, the process of incinerating waste is often divided into four phases: Drying-out, ignition, combustion and burning- out.
  • slag chute or shaft When the material has been burned out, it is discharged from the end of the burning-out grate or grates into a slag chute or shaft.
  • the slag accumulates in the slag chute or shaft and is disposed of by being deposited or re-used, e.g. in building material ⁇ .
  • the minimum time required for a sufficient burning-out of the waste can vary considerably, depending on the nature and condi ⁇ tion of the waste.
  • the incineration of waste requires the temperature to be held within reasonable limits, of which the upper limit is set in consideration of the incineration plant. Further, there is also a lower limit for the speed, with which the waste can be conveyed through the incineration plant, depending on the nature and condition of the waste, including the humidity, the degree of agglomeration or the degree of looseness.
  • waste in a combined power and heating station makes it desirable that the waste can be used in the manner of an ordinary fuel capable of being supplied in dependence on the instantaneou ⁇ energy being drawn from the power and heating station and varying through the twenty-four hours of the day and night, with a view to an optimum and maximum exploitation of the plant and the calorific value of the waste.
  • Thu ⁇ the operation of the plant depends to a high degree on the ability of the operator to convert imperfect information into oper ⁇ ational parameters, and in the case of too much or too little fuel being supplied to the process of combustion, this will in the first instance (after 15-60 minutes) manifest itself as changes in temperatures and in energy production, likewise the content of i.a. N0 ⁇ and CO in the flue gas and the content of un-combusted material in the slag. In the long run this will cau ⁇ e damage to the boiler and the ma ⁇ onry.
  • Thu ⁇ in the commonly known ⁇ y ⁇ tem ⁇ , it is left to the operator e.g. to recognize the presence of moist waste having a high specific weight and a tendency toward agglo ⁇ meration, and to take the requi ⁇ ite control measures, e.g. changing the speed of the infeed grate and the quan ⁇ tity and temperature of the air for combustion.
  • infeed problems can also arise that are difficult to detect in time by visual monitoring, e.g. due to for ⁇ mation of bridges in the waste in the waste chute or shaft or wedging-together of the waste below the infeed arch, or waste getting stuck on the travelling grate, the latter especially being a problem with travelling grates having a number of movable grate beams.
  • the problems with the infeed of waste getting stuck in the fuel chute or shaft can be difficult to recognize visually before a change in the proce ⁇ of combustion takes place.
  • the embodiment set forth in claim 2 is especially well- -suited for detecting infeed problems in the fuel chute or shaft, because it can detect changes in the ma ⁇ being applied to the infeed grate from the fuel chute or ⁇ haft relatively quickly.
  • the weight being mea ⁇ ured can be included in the computation of the ⁇ peci ⁇ fic weight of the wa ⁇ te, when the geometry of the fuel chute or ⁇ haft i ⁇ known and the height of the filling in the fuel chute or shaft has been observed or measured.
  • the arrangement according to the embodiment set forth in claim 3 is i.a. well- ⁇ uited where the weighing cell i ⁇ to mea ⁇ ure the quantity of wa ⁇ te lying loo ⁇ e on the infeed grate without a ⁇ imultaneous load from the fuel chute or shaft.
  • this embodiment is advantageous when combined with additional weighing cells in the other end of the grate, as the signal ⁇ from the two mea ⁇ uring point ⁇ may be u ⁇ ed for indicating problem ⁇ with the infeed or sudden changes in the specific weight, because the meas ⁇ uring signals indicate a change in the distribution of mass. This may e.g. be due to waste having got stuck so that waste is accumulated at the upstream end of the grate and that the downstream end is empty. If the signals show a change in the opposite sense, this could indicate that no waste is being supplied or that the waste being supplied has a small mass.
  • the embodiment set forth in claim 5 is especially advan ⁇ tageous in combination with drive mechanisms having a sub ⁇ tantial extent in the longitudinal direction of the grate, such as i ⁇ the ca ⁇ e when using a grate with two movable ⁇ et ⁇ of grate beam ⁇ of the kind known e.g. from Dani ⁇ h Patent Application No. 0647/94, having a drive shaft for each set of grate beams, the shafts being mu ⁇ tually offset.
  • the present invention also relates to a method of using the arrangement according to the invention.
  • Thi ⁇ method is of the kind ⁇ et forth in the preamble of claim 6, and according to the invention it al ⁇ o comprises the steps set forth in the characterizing clause of this claim 6.
  • thi ⁇ unit can compute the instantaneous value of the mas ⁇ flow of the quantity of waste being supplied, as indicated in claim 11 on the basis of signals indicating the speed of the grate.
  • control and/or monitoring unit can deliver an alarm signal to the operating person ⁇ nel or automatically initiate function ⁇ adapted to ⁇ olve the problem having ari ⁇ en, or give the combu ⁇ tion process an advance warning of a change in the nature of the waste.
  • the control and/or monitoring unit can use this signal for monitoring the degree of filling of the fuel chute or shaft, ⁇ o that the signal can be used for controlling the supply to the fuel chute or shaft.
  • a mea ⁇ suring signal is provided that expresses the mass of wa ⁇ te clo ⁇ e to the combustion space, and thi ⁇ measuring ⁇ ignal can be used in an improved manner by the control and/or monitoring unit for computing the speed of ⁇ up- plying wa ⁇ te to the combu ⁇ tion process, and this process may be optimized by including the computation in the control of the speed of the infeed grate in the manner set forth in claim 12, or else in the control of the combustion in the manner set forth in claim 13.
  • the loading of the weighing cells below this part is an ex ⁇ pression of the specific weight of the waste. This waste is about to enter into the combu ⁇ tion process in a few moments' time, for which reason such information is very valuable.
  • Figure 1 i ⁇ an overall diagrammatic ⁇ ketch ⁇ howing the principles of a waste-incineration plant
  • Figure 2 shows a con ⁇ truction of a grate ⁇ ystem consi ⁇ ting of five ⁇ ection ⁇ adapted for u ⁇ e in a wa ⁇ te-incineration plant
  • Figure 3 i ⁇ a simplified side view of an individual grate beam in the sy ⁇ tem of Figure 2
  • Figure 4 ⁇ hows the construction of the drive mechanism for a grate comprising two sets of movable grate blocks
  • Figure 5 shows how, according to the present invention, a grate is supported by weighing devices
  • Figure 6 is a front view showing how, according to the present invention, weighing devices are placed at the outlet end of the grate-supporting arrangement of Figure 5.
  • FIG 1 is a diagram showing a waste-incineration plant, in which a vehicle A can unload wa ⁇ te into an unloading ⁇ ilo B, from which waste can be taken by a crane C and supplied to the incineration plant through a feed hopper D, from which the waste falls down into a fuel chute E, at the same time functioning as a buffer store for waste to an infeed grate R ⁇ hown in Figure 2, situated in the bottom of the fuel chute E.
  • the infeed grate R convey ⁇ the wa ⁇ te into the combu ⁇ tion chamber F, in which the waste is incinerated and finally di ⁇ charged a ⁇ ⁇ lag from the grate system at the slag chute S.
  • the flue gases themselves are conducted further to the boiler part K with a temperature typically in the interval 850- 1050°C, in which the energy content of the flue gases is utilized. Then, the flue gases are conducted further with a lower temperature of typically 180-250°C to the flue-gas cleaner L, in which ⁇ olid particles and pos ⁇ ibly other ⁇ ubstances are filtered out of the flue gases, after which the latter are transported further by means of the fan M to the chimney N and discharged to atmos ⁇ phere.
  • the substances being discharged in the form of slag and flue gases are as environmentally neutral as pos ⁇ ible. With regard to the slag, this mean ⁇ that i.a.
  • organic substances are either incinerated or sterilized to kill contaminating bacteria and germ ⁇ , and that the content of heavy-metal compounds and other substances is as low as possible, which conditions are best achieved by mean ⁇ of an effective uniform incineration.
  • flue gas it is likewise be ⁇ t ensured that the content of i.a. dioxines, carbon monoxide and NO x i ⁇ as low a ⁇ possible by means of an effective uniform incineration.
  • FIG. 2 show ⁇ the grate system in the combustion chamber F.
  • This grate system may be divided into an infeed grate R and four succeeding grates as shown in the drawing for conveying the waste through the proce ⁇ of incineration.
  • Thi ⁇ proce ⁇ of incineration can typically be divided into four phases: I drying-out, II ignition, III combus- tion and IV burning-out, and the grate system may be divided into a greater or smaller number of grate sec ⁇ tions.
  • the individual grate section ⁇ are con ⁇ tructed with travelling grates consisting of two sets of grate parts, of which at least one is movable as represented by the grate beam 1 in the grate section II, while the other grate parts may be stationary as represented by the grate beam 1 in the grate section I; the functioning of these travelling grates will be explained in more detail below.
  • waste is introduced from a fuel chute (not ⁇ hown) .
  • the infeed grate R is "travelling", it withdraws waste from the bottom of the waste chute E and moves it forward and downward in the direction towards the right in the drawing.
  • the waste is "torn open” by the infeed grate R so that it begins to distribute itself evenly over the infeed grate R, and is supplied with air from outside.
  • the waste After having passed the infeed grate R, the waste is transferred to the grate section I and is supplied with additional air, air being conducted along and above the grate in section I and blown up through the grate from the primary-air chamber P, respectively.
  • This treatment with air provides a continued drying-out of the moisture content in the wa ⁇ te, a ⁇ already started on the infeed grate.
  • the waste After having pas ⁇ ed the grate in the grate section I, the waste is transferred to the grate in the grate section II. In this section, the waste is conveyed further in the forward direction, during which the temperature in- crea ⁇ es, so that ignition of the waste is started, if ⁇ uch ignition has not already occurred on the infeed grate or in the grate ⁇ ection I. During this conveying, the tearing-open of the waste by the grate is continued.
  • the wa ⁇ te After the incineration on the grate section ⁇ I+II+III, the wa ⁇ te is transferred to the burning-out section IV, on which combustible residue i ⁇ burned out. After having pa ⁇ ed through the grate ⁇ ection IV, the wa ⁇ te, now being completely burnt-out, is discharged in the form of slag in the slag chute S.
  • Figure 3 shows a movable grate beam 1 corresponding to the one shown in grate section II in Figure 2.
  • grate blocks 3 adapted to be in contact with the waste, are placed.
  • This grate beam is assembled to ⁇ gether with a number of grate beams extending parallel to it, so a ⁇ to form a grate.
  • a second grate or grate part i ⁇ placed, e.g. in the form of a stationary grate like the one shown in grate section I in Figure 2.
  • the movable grate shown in Figure 3 executes upward and forward progressing pendular movements produced by supporting the grate beam 1 on the periphery of a shaft in the recess 7.
  • the other end of the grate beam 1 is movably supported through a footpiece 13, allowing the grate beam to execute reciprocating movements, also allowing thermal expansion in it ⁇ longi ⁇ tudinal direction.
  • the movable grate will, through it ⁇ upward and forward progre ⁇ ing wave movement, move forward from the plane formed by the second grate and lift the waste and convey it forward through a short di ⁇ tance.
  • the movable grate After thi ⁇ , the movable grate will de ⁇ cend below the plane formed by the ⁇ econd grate, ⁇ o that the wa ⁇ te will be ⁇ upported by the latter, and then, the movable grate will execute a downward and rearward wave movement, after which the procedure i ⁇ repeated.
  • the waste resting on the grate will alternately be lifted and lowered.
  • the alternate lifting and lowering of the grate and the wa ⁇ te referred to above will transfer large pulsating loads to the ⁇ upport ⁇ for the grate, and in the previou ⁇ ly known technology, the primary purpose of the means sup- porting the grate has been to support the grate without transmitting vibrations to the surrounding structural parts.
  • the supporting means are primarily constructed with a view to creating a secure foundation.
  • Figure 4 shows the drive mechanism for the grate beams in such a doubly-movable grate.
  • the second grate beam 2 belonging to the second grate part is sup ⁇ ported by a second shaft 10 through a second carrier 12 in a recess 8.
  • the grate part comprising the grate beam ⁇ 1 and 2 will alternately exe- cute an upward and forward progressing movement, ⁇ o that the wa ⁇ te will be conveyed alternately by the first grate part and the second grate part.
  • a more uniform conveying and les ⁇ vibrations are achieved, i.a. because the lifting heights may be reduced to one- -half when the grate parts move in counter-phase.
  • the travelling grate ⁇ are primarily con ⁇ tructed with a view to conveying the wa ⁇ te and to be able to withstand the loads, to which they are subjected, as well as to tear-open and distribute the waste over the grate in order to facilitate the in ⁇ cineration and make it uniform.
  • the travelling grates are ⁇ ubjected to large mechanical loads, since they must be able to carry and lift all the waste resting upon them, and especially the travelling grate situated below the fuel chute and constituting the infeed grate R may be subjected to the total weight of the waste being pres ⁇ ent in the fuel chute.
  • This grate must be able to accommodate the full longitudinal expansion caused by the thermal influence from a cold start to the full operational temperature.
  • the grates as such must be constructed so as to be able to tear-open the waste and distribute it over the grate in the optimum manner without the wa ⁇ te getting stuck in the grate; such waste may e.g. consist of larger parts of furniture and fine dust as well as ashes. Further, the grates must be made of a material being able to with- stand the aggressive gase ⁇ being produced during the proce ⁇ of combustion in the best possible manner. At the same time, the movable parts mu ⁇ t be constructed with a view to countering and resi ⁇ ting wear cau ⁇ ed by du ⁇ t and a ⁇ he ⁇ in the best possible manner.
  • the present invention is ba ⁇ ed upon the idea of including the infeed grate R and/or other grates in the form of travelling grates in the production of parameters by providing these grates with a weighing-cell arrangement and using the weight ⁇ ignal ⁇ produced for deriving addi ⁇ tional parameter ⁇ for use in the control and monitoring.
  • wa ⁇ te material can ⁇ upport a combu ⁇ tion proce ⁇ if it contains at least 25% combustible matter, this meaning that a completely burned-out slag being discharged to the slag chute may have a residual weight constituting from 0 to 75% of the weight of the mass of waste material being supplied, typically 25%.
  • the useful calorific value can vary considerably due to variations in the water content, and in this case a rule-of-thumb indicates that waste material with a water content of up to 50% can support a combustion pro ⁇ cess.
  • the weight measure ⁇ ments are provided by supporting the travelling grate on weighing cells (also called load cells) .
  • weighing cells also called load cells
  • a preferred embodiment for providing such weighing arrangement in the form of weighing cells 20a, 20c & 20d is shown in Figure 5.
  • the supporting structure generally designated U, supports a doubly moving travelling grate having grate beams 1, 2 of the kind shown in Figure 3, and is provided with drive arrangements 7-12 as shown in Figure 4.
  • the drive shafts 9, 10 are supported in the supporting structure U in flange bearings 15, 16, and the footpieces 13 are supported on a supporting beam 14, in the drawing being shown with an H-shaped profile.
  • the supporting beam 14 is supported on the weighing cells 20a and 20b, as al ⁇ o shown in front view in Figure 6.
  • the supporting beam 14 is only ⁇ upported in the vertical direction by the weigh ⁇ ing cells 20a-20d, while in the other directions, it is guided by guides 18, the latter by means of eye links allowing movement in the vertical direction only.
  • the guide 18 at one end of the beam 14 prevents that end from moving in the longitudinal direction of the beam, while the guide 18 at the other end allows a certain longitudinal displacement of the beam so a ⁇ to accommodate thermal expansion of the latter.
  • the weighing cells are supported on brackets 19a and 19b, the latter being supported below.
  • This construc ⁇ tion with a supporting beam 14 supported in the vertical direction at both ends through respective weighing cells 20a, 20b and guided by a guide 18 solely allowing vertical movement ⁇ at one end of the ⁇ upporting beam 14, in the other end having a certain clearance in the longitudinal direction of the supporting beam 14 for accommodating thermal expansion, is especially well- ⁇ uited for producing weight ⁇ ignals for weight distributions susceptible to variations transver ⁇ ely of the travelling grate.
  • the guides 18 allow thermal expansion to be accommodated at the measuring device. With the guides 18 shown, it is, however, possible to increase the extent of the supporting beam 14 in the vertical direction with a view to shielding the weighing cells from the influence of heat from above, without compromising the capacity of the guide ⁇ 18 to guide the supporting beam 14.
  • the ⁇ haft ⁇ 9, 10 in the driving arrangement are ⁇ upported in flange bearings 15, 16, the latter being ⁇ upported vertically on four weighing cells, of which only the two, 20c, 20d on one side, are ⁇ hown.
  • Thi ⁇ construction is especially well-suited for operation with vertical loads moving longitudinally and tran ⁇ ver ⁇ ely of the travelling grate ⁇ , ⁇ uch a ⁇ is the ca ⁇ e with the driving arrangement for a doubly movable travelling grate as ⁇ hown.
  • the flange bearings 15, 16 are supported on the side wall 17, the latter transferring the force ⁇ down- wardly to bracket ⁇ 25, that may have a ⁇ imilar shape as the brackets 19a, 19b in the weighing arrangement de ⁇ ⁇ cribed above.
  • the bracket ⁇ 25 are secured to reinforce ⁇ ments 27 on the side wall 17. From the brackets 25, the vertical forces are transferred to the weighing cells 20c, 20d, a similar arrangement being present on the other side (not shown) . Downwardly, the weighing cells 20c, 20d are supported on columns 21, 22 with H-shaped profiles.
  • the function of guiding the side wall 17 and the bracket 25 is provided by the reinforcement 27 and other reinforcements (not shown) on the side wall 17.
  • the reinforcement 27 is connected to a guide 24 preventing movement of the reinforcement 27 in its longitudinal direction and with a guide 23 situated above the guide 24 at the upper part of the side wall 17, in this location allowing vertical movements but at the same time preventing the ⁇ ide wall 17 from moving in directions at right angles to the plane of the drawing.
  • An additional guide 23 situated oppositely on the upper side of the side wall ⁇ 17 allows a certain movement in the vertical and longitudinal directions.
  • this embodiment will comprise a total of four weighing cells, of which only the two designated 20c and 20d are visible in Figure 5, making it po ⁇ ible to obtain correct measurements of force ⁇ moving in two dimensions, because the sum total of the weighing signals from the four weighing cells will always repre ⁇ ent the correct value for the total load. It is also possible to produce the weighing signals by using three weighing cells, but this simplification of the weighing cells would produce a more complicated ⁇ upporting arrangement than that achieved in a ⁇ imple manner by u ⁇ ing the ⁇ ide walls 17. With the embodiments shown, it is pos ⁇ ible to achieve a correct weighing of a load moving in one and two dimen ⁇ sions, respectively, at right angles to the vertical.
  • a travelling grate being u ⁇ ed a ⁇ an infeed grate R in incineration plant ⁇ and being provided with one or a number of weighing cell ⁇ placed at one end or both end ⁇ can advantageou ⁇ ly be used at a number of locations in the infeed-grate line in a waste-incineration plant.
  • an infeed grate R provided with one or a number of weighing cell ⁇ 20 in the end clo ⁇ e ⁇ t to the infeed of wa ⁇ te can produce a weight signal being mainly a function of the force exerted on the grate R by the waste being pre ⁇ ent in the fuel chute E.
  • This weight signal can at an early moment in time give a warning about bridge formation or other blockage in the fuel chute beginning to take place, because such a blockage will cause the weight ⁇ ignal being produced to show a decrease without a simultaneous reduction of the height of the filling in the fuel chute E.
  • it will be pos ⁇ ible to take remedial action with a view to breaking the blockage before the latter can be interpreted a ⁇ a lack in the supply of waste to the infeed grate R.
  • Thi ⁇ weight ⁇ ignal can also be used to provide information about the consistency of the waste, becau ⁇ e the volume of the waste in the fuel chute E can be computed on the basis of the geometry of the fuel chute and the filling height of the fuel in the fuel chute E.
  • information about the weight is provided, it is po ⁇ ible to calculate the aver ⁇ age specific weight.
  • This information about the specific weight can be used to make an estimate of the mass of waste being advanced by the infeed grate R at a given speed.
  • the specific weight can also be used to make an estimate of the water content in the waste. This can e.g. take place in connection with a visual inspection, in which the waste in general has been identified; e.g.
  • thi ⁇ weight ⁇ ignal may be used to provide a better estimate of the mass flow of waste on the infeed grate R. Further, this signal may be used to give an early warning that wa ⁇ te ha ⁇ got stuck on the infeed grate R, since waste getting stuck in the infeed grate R will produce a blockage of the subsequently arriving waste and thu ⁇ cause waste to ac ⁇ cumulate on the infeed grate R upstream of the place at which the waste ha ⁇ become ⁇ tuck.
  • the volume of unloaded waste will be known. This known volume can be used for computing the instantaneous specific weight of the waste when its weight i ⁇ measured by one or a number of weighing cell ⁇ 20 ⁇ ituated downstream of the infeed arch or beam. If the weighing cell or cells is/are situated at a grate down ⁇ tream of the infeed grate R and the infeed arch or beam and are being driven with a different ⁇ peed, the volume will, of cour ⁇ e, be corrected inver ⁇ ely proportio ⁇ nal to the ⁇ peed ratio.
  • the succeeding grate ⁇ are provided with weigh ⁇ ing cell ⁇ , the latter can - in addition to providing alarm ⁇ ignal ⁇ about infeed problem ⁇ - provide information about the proces ⁇ of combu ⁇ tion, e ⁇ pecially the reduction in weight occurring through drying-out and combu ⁇ tion, re ⁇ pectively.
  • Thi ⁇ information can e.g. be used for deter ⁇ mining the maximum speed of the infeed grate R and/or the remaining grates. This maximum speed may e.g. be divided into two levels, one level being a maximum normal operating speed and the other being a maximum peak-load speed.
  • the maximum normal operating speed may be deter ⁇ mined on the condition that no sub ⁇ tantial reduction of weight in the waste must occur during the burning-out in the grate section IV. This may be achieved by the control and monitoring unit ⁇ ignalling to the operator that he i ⁇ free to control according to other parameter ⁇ , ⁇ ince the incineration of the waste takes place safely and completely.
  • the maximum peak-load speed may be determined on the condition that the reduction of weight during the burning-out in the grate section IV must not exceed a value forming a certain ratio with the reduction of weight occurring during the combustion in the grate section III. Thu ⁇ , the reduction of weight during the burning- out may e.g. be set to 20% of the reduction in weight occurring during the combustion. Thi ⁇ may e.g.
  • the reduction in weight being computed from weight signals from the inlet and outlet end of the individual grate, and the reduction of weight during the combustion proce ⁇ is related to the reduction in weight during the burning-out proces ⁇ .
  • the control function or the oper- ator i ⁇ free with regard to excercising control according to other parameters, but if this value i ⁇ reached, the weight ⁇ ignal ⁇ can be u ⁇ ed to control the speed of the grates so as to maintain thi ⁇ ratio.
  • the parameter ⁇ derived from the weight ⁇ ignal ⁇ will take over the control of the speed of the infeed grate R, possibly also that of the succeeding grate, as well as the process of combustion, so that the weight signal ⁇ now constitute the primary control signals with regard to the combustion proce ⁇ s.
  • the maximum speed for the grate sy ⁇ tem can also be determined based on a desired reduction in weight of the waste from the feeding-in to the fuel chute E to the di ⁇ charge through the slag chute S.
  • Thu ⁇ e.g. large reduction ⁇ in weight from the feeding- -in to the termination of the combu ⁇ tion proce ⁇ a ⁇ such can indicate a great proportion of combustible matter in the wa ⁇ te, and the ⁇ peed of the infeed grate can be reduced correspondingly.
  • a small reduction in weight may indicate a ⁇ mall proportion of combu ⁇ tible matter and/or matter that will not burn ea ⁇ ily in the wa ⁇ te, and this signalling can be used for immediately reducing the speed of the infeed grate and initiate the feeding-in of alternative fuel, e.g. in the form of gas or coal, with a view to maintaining the production of energy and at the same time retain a complete burning- out of the waste.
  • alternative fuel e.g. in the form of gas or coal
  • the combustion proces ⁇ i ⁇ run under normal operating condition ⁇ in which the energy content per mas ⁇ unit of waste is taken to be constant.
  • the speed of the infeed grate R is controlled on the background of the weight signals and the calculated specific weight of the waste in the fuel chute E, ⁇ o that a constant mas ⁇ flow of material i ⁇ delivered from the fir ⁇ t infeed grate R.
  • the succeeding grates are controlled with a speed, according to experi ⁇ ence providing optimum combustion.
  • the weight measurement according to the invention provide ⁇ ⁇ ubstantially improved controlled parameters, that can advantageously be included in the parameters u ⁇ ed for controlling the process of combustion and the supply of energy from a combined power and heating station using waste a ⁇ it ⁇ fuel.
  • the weight ⁇ ignal ⁇ produced by the weighing cell ⁇ at the travelling grates are influenced by the vibrations occur ⁇ ring during the operation of the travelling grate, for which reason they must be filtered and/or averaged. This may advantageously occur in synchronism with the speed of the travelling grate, so that the time constants of a filter are varied in proportion to the cycle time (1/ ⁇ peed) of the travelling grate. With thi ⁇ arrangement it is achieved that when the dead time for producing the weight signals varie ⁇ proportionally with the ⁇ peed, the points with which the weight signals are related will always be in the same location on the travelling grate.
  • the weighing cell can be composed of a number of weighing cell ⁇ connected in ⁇ erie ⁇ , so as to make them function as if they were ⁇ tacked.
  • the most sensitive weighing cell in the series connection will produce the weight signals in a first, lowermost interval for loads, and when the limiting value for load ⁇ in thi ⁇ first lowermost interval is ex ⁇ ceeded, the weight signals from the second most sensitive weighing cell are used, so that it is possible to achieve accurate measurement ⁇ at ⁇ mall load ⁇ and still retain the maximum measurable load.
  • the switching between the weight signal ⁇ from the various weighing cells in the series connection does, of course, not necessarily have to be carried out in the form of a complete switching at a certain limiting value, but may also be carried out gradually by varying the weighting of the signals from the individual weighing cells in the series connection.

Abstract

In an arrangement with a grate in an incineration plant, especially a waste-incineration plant, in which plant weighing of the fuel is carried out and at least one grate is used for conveying fuel, especially waste, from a fuel supply (E) to a combustion space (F), especially for use in plants using one or a number of grates for conveying fuel through the combustion space (F) and further to the slag discharge (S), said grate or grates being of the travelling-grate type and comprising at least one movable grate part (1), the main novel feature is that at least one travelling grate is supported on at least one weighing cell (20) capable of producing a signal representing the instantaneous value of the weight, with which the weighing cell is loaded. The weighing signal or signals is/are used to provide information about and to control the supply of fuel and the process of combustion.

Description

ARRANGEMENT WITH AN INFEED GRATE IN AN INCINERATION PLANT. ESPECIALLY A WASTE-INCINERATION PLANT. AND METHOD OF USING SAID ARRANGEMENT
TECHNICAL FIELD
The present invention relates to an arrangement with a grate in an incineration plant, especially a waste-in¬ cineration plant, in which at least one grate is used for conveying fuel, especially waste, from a fuel supply to a combustion space, especially for plants in which at least one grate is used for conveying fuel through the combustion space and further to the slag discharge, said grate or grates being of the travelling-grate type with at least one movable grate part.
BACKGROUND ART
In incineration plants for incinerating household and industrial waste, waste having been weighed is transferred to an unloading silo. When it is to be transferred to the combustion plant as such, the waste is taken up from the unloading silo, normally by using a conveyor belt or a crane, the waste being weighed at the same time. This weight measurement is transferred to the superior moni¬ toring system, making it possible to monitor the quantity of waste being incinerated in each incineration line. The waste is delivered to the incineration plant as such through a filling hopper, after which it falls down into a fuel chute or shaft (waste chute or shaft) constituting a buffer store. An infeed grate in the form of a travel- ling grate is situated in the bottom of the fuel chute or shaft and adapted to remove the waste from the bottom of the fuel chute or shaft.
The waste having been taken out from the bottom of the fuel chute or shaft and having been compacted by the waste lying on top of it in the chute or shaft, becomes more loose during the conveying on the infeed grate, because the latter being of the travelling-grate type tears the waste open, so that the latter will distribute itself more loosely and uniformly during the conveying on the infeed grate or grates. Normally, the infeed grate will be succeeded by at least one grate in a combustion cham¬ ber, in which the waste is incinerated while air for combustion is supplied, partly in the form of primary air from below through the grate, partly in the form of secondary air to the combustion chamber.
The calorific value is normally low compared to other types of fuel, and the burning-out time may differ greatly for the individual components of the waste. The lower calorific value, i.e. the net contribution of energy per kg fuel, i.e. including losses due to heating-up and evaporation of water content, can typically have a value of 8,000 kJ/kg; this εhould be compared to the calorific value of plastic in the form of polyethylene of up to 44,800 kJ/kg and coal of up to 29,300 kJ/kg. Because of the water content and the burning-out time of the waste, the process of incinerating waste is often divided into four phases: Drying-out, ignition, combustion and burning- out. It may also be necessary to add water, if the waste has a high calorific value, or to add fuel, if the calo¬ rific value is too low. When the material has been burned out, it is discharged from the end of the burning-out grate or grates into a slag chute or shaft. The slag accumulates in the slag chute or shaft and is disposed of by being deposited or re-used, e.g. in building materialε.
In consideration of the effect on the environment from the residual product in the form of slag from the in¬ cineration, it is of substantial importance that the burning-out of the waste has taken place at a sufficiently high temperature.
With regard to temperature, however, masonry and boiler as well as aggressive flue gases and fluctuations in the temperature of the flue gas determine a higher limit for the temperature, at which the waste can be incinerated, typically in the interval 850-1050°C.
Further, with a given combustion temperature, the minimum time required for a sufficient burning-out of the waste can vary considerably, depending on the nature and condi¬ tion of the waste.
Further, it is of decisive importance for the possibility of reducing the production of dioxines, carbon monoxide and N0X being discharged as flue gas, that the process of combustion is stabilized with regard to temperature and oxygen concentration, since it is widely known that the production of these substances increases markedly with sudden changes in the operating conditions.
Thus, the incineration of waste requires the temperature to be held within reasonable limits, of which the upper limit is set in consideration of the incineration plant. Further, there is also a lower limit for the speed, with which the waste can be conveyed through the incineration plant, depending on the nature and condition of the waste, including the humidity, the degree of agglomeration or the degree of looseness.
While the heat produced in the waste-incineration plant was previously used only for heating high-temperature boiler plants for supplying the district-heating network, this heat is now commonly used for producing steam in combined power and heating stations supplying both dis¬ trict heating and electrical power, and this is a step forward both with regard to the economy and to the en¬ vironment. The operation of such waste-burning combined power and heating stations has, however, led to increased demands to the utilization of the energy in the fuel or the efficiency of the incineration plant, and to the stability in the energy production.
Thus, the use of waste in a combined power and heating station makes it desirable that the waste can be used in the manner of an ordinary fuel capable of being supplied in dependence on the instantaneouε energy being drawn from the power and heating station and varying through the twenty-four hours of the day and night, with a view to an optimum and maximum exploitation of the plant and the calorific value of the waste.
Available for controlling these processes are the oper- ational parameters for the steam plant and the energy production of the power and heating station, as well as some parameters from the incineration plant, usually comprising the temperatures in the combustion chamber, after-burning chamber, boiler etc., 02~content in the flue gas as well as from visual monitoring of the process of combustion per se, the waste being supplied and the slag being discharged. These parameters are converted automatically or by an operator empirically into control parameters, i.e. damper positions, grate speeds etc., including posεibly pre-heating of air. Thuε, the operation of the plant depends to a high degree on the ability of the operator to convert imperfect information into oper¬ ational parameters, and in the case of too much or too little fuel being supplied to the process of combustion, this will in the first instance (after 15-60 minutes) manifest itself as changes in temperatures and in energy production, likewise the content of i.a. N0χ and CO in the flue gas and the content of un-combusted material in the slag. In the long run this will cauεe damage to the boiler and the maεonry.
Problems with slag not having been burnt-out completely may i.a. be due to an excesεive maεε of waεte being con- veyed through the combustion chamber and/or that the waste is conveyed too fast through thiε chamber. This can easily happen, even though the weight of waste being supplied to the fuel chute or shaft is known, because this is still an incomplete parameter, e.g. not indicating the specific weight of the material present in the fuel chute; e.g. moist waste will have a high specific weight and tend to compress the lowermost waεte in the waste chute or shaft, in which the moist waεte additionally tends to agglomerate and hence is difficult to burn.
Thuε, in the commonly known εyεtemε, it is left to the operator e.g. to recognize the presence of moist waste having a high specific weight and a tendency toward agglo¬ meration, and to take the requiεite control measures, e.g. changing the speed of the infeed grate and the quan¬ tity and temperature of the air for combustion.
Thus, there exists a need for providing additional para- meters relating to the nature and condition of the waste and to the combustion procesε for controlling the opera¬ tion of the plant.
Further, infeed problems can also arise that are difficult to detect in time by visual monitoring, e.g. due to for¬ mation of bridges in the waste in the waste chute or shaft or wedging-together of the waste below the infeed arch, or waste getting stuck on the travelling grate, the latter especially being a problem with travelling grates having a number of movable grate beams. Eεpecially the problems with the infeed of waste getting stuck in the fuel chute or shaft can be difficult to recognize visually before a change in the proceεε of combustion takes place. Thus, also in this regard it is desirable that an early warning of problems in the fuel chute or shaft can be provided.
DISCLOSURE OF THE INVENTION
It is the object of the present invention to remedy the problems with the known technology and to make it easier to control the proceεε of combustion, at the same time exploiting the latter in the best possible manner without lowering the quality of the slag.
This object is achieved with an arrangement of the kind set forth in the preamble of claim 1, according to the present invention being characterized by the features set forth in the characterizing clauεe of this claim 1.
With this arrangement, it is posεible to provide a signal expresεing the weight of the maεε of waεte lying on the travelling grate, so that the instantaneous mass flow to the combustion space can be computed on the basis of information about the speed of the grate, and so that the instantaneous value of the masε being fed in may be included in the control function instead of an estimated mass, thus facilitating the control of the combustion process. Further, it is possible to detect infeed problems and/or changes in the specific weight of the waste as changes in the weight being measured, this posεibly being used in conjunction with other changes in the operating conditions.
The embodiment set forth in claim 2 is especially well- -suited for detecting infeed problems in the fuel chute or shaft, because it can detect changes in the maεε being applied to the infeed grate from the fuel chute or εhaft relatively quickly. At the εame time, the weight being meaεured can be included in the computation of the εpeci¬ fic weight of the waεte, when the geometry of the fuel chute or εhaft iε known and the height of the filling in the fuel chute or shaft has been observed or measured.
The arrangement according to the embodiment set forth in claim 3 is i.a. well-εuited where the weighing cell iε to meaεure the quantity of waεte lying looεe on the infeed grate without a εimultaneous load from the fuel chute or shaft. Further, this embodiment is advantageous when combined with additional weighing cells in the other end of the grate, as the signalε from the two meaεuring pointε may be uεed for indicating problemε with the infeed or sudden changes in the specific weight, because the meas¬ uring signals indicate a change in the distribution of mass. This may e.g. be due to waste having got stuck so that waste is accumulated at the upstream end of the grate and that the downstream end is empty. If the signals show a change in the opposite sense, this could indicate that no waste is being supplied or that the waste being supplied has a small mass.
In the embodiment set forth in claim 4 it is avoided that the weighing cell is relieved by guides, or that it is subjected to an oblique force, which the weighing cells cannot meaεure directly.
The embodiment set forth in claim 5 is especially advan¬ tageous in combination with drive mechanisms having a subεtantial extent in the longitudinal direction of the grate, such as iε the caεe when using a grate with two movable εetε of grate beamε of the kind known e.g. from Daniεh Patent Application No. 0647/94, having a drive shaft for each set of grate beams, the shafts being mu¬ tually offset. This makes it poεεible to place the weigh¬ ing cells in the vicinity of reεpective cornerε in a rectangular plane, εo that the individual weighing cells are not subjected to forces deviating substantially from the vertical.
The present invention also relates to a method of using the arrangement according to the invention. Thiε method is of the kind εet forth in the preamble of claim 6, and according to the invention it alεo comprises the steps set forth in the characterizing clause of this claim 6. By supplying the weighing εignal being produced to a control and/or monitoring unit, thiε unit can compute the instantaneous value of the masε flow of the quantity of waste being supplied, as indicated in claim 11 on the basis of signals indicating the speed of the grate.
By proceeding in the manner εet forth in claim 7 it iε poεsible to trace variationε occurring becauεe of forma¬ tion of bridges in the waste in the waste chute or shaft or wedging-together of the waste below the infeed arch or the infeed beam, and the control and/or monitoring unit can deliver an alarm signal to the operating person¬ nel or automatically initiate functionε adapted to εolve the problem having ariεen, or give the combuεtion process an advance warning of a change in the nature of the waste. Another possibility is for the control and/or monitoring unit to use this signal for monitoring the degree of filling of the fuel chute or shaft, εo that the signal can be used for controlling the supply to the fuel chute or shaft.
By proceeding in the manner set forth in claim 8 it is posεible to compute the specific weight of the waste, and an eεti ate of e.g. the humidity in the waεte can be made on the baεis of experience and posεibly also visual inspection. As εet forth in claim 12 it is also poεεible to uεe the value determined for the εpecific weight for controlling the speed of the infeed grate.
By proceeding in the manner set forth in claim 9, a mea¬ suring signal is provided that expresses the mass of waεte cloεe to the combustion space, and thiε measuring εignal can be used in an improved manner by the control and/or monitoring unit for computing the speed of εup- plying waεte to the combuεtion process, and this process may be optimized by including the computation in the control of the speed of the infeed grate in the manner set forth in claim 12, or else in the control of the combustion in the manner set forth in claim 13.
Because the volume of the waste lying loosely on that part of the infeed grate or a succeeding grate closest to the furnace space can be considered as known, the loading of the weighing cells below this part is an ex¬ pression of the specific weight of the waste. This waste is about to enter into the combuεtion process in a few moments' time, for which reason such information is very valuable.
By proceeding in the manner set forth in claim 10 it is possible to use a change in the distribution of weight on an infeed grate or a number of infeed grates used for signalling irregularities when processed in the control and/or monitoring unit.
BRIEF DESCRIPTION OF THE DRAWING
In the following detailed part of the present descrip¬ tion, the invention will be explained in more detail with reference to the exemplary embodimentε of a waεte- -incineration plant and parts used therein εhown in the drawingε, in which
Figure 1 iε an overall diagrammatic εketch εhowing the principles of a waste-incineration plant, Figure 2 shows a conεtruction of a grate εystem consiεting of five εectionε adapted for uεe in a waεte-incineration plant,
Figure 3 iε a simplified side view of an individual grate beam in the syεtem of Figure 2, Figure 4 εhows the construction of the drive mechanism for a grate comprising two sets of movable grate blocks, Figure 5 shows how, according to the present invention, a grate is supported by weighing devices, and Figure 6 is a front view showing how, according to the present invention, weighing devices are placed at the outlet end of the grate-supporting arrangement of Figure 5.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 is a diagram showing a waste-incineration plant, in which a vehicle A can unload waεte into an unloading εilo B, from which waste can be taken by a crane C and supplied to the incineration plant through a feed hopper D, from which the waste falls down into a fuel chute E, at the same time functioning as a buffer store for waste to an infeed grate R εhown in Figure 2, situated in the bottom of the fuel chute E. After this, the infeed grate R conveyε the waεte into the combuεtion chamber F, in which the waste is incinerated and finally diεcharged aε εlag from the grate system at the slag chute S. The flue gases themselves are conducted further to the boiler part K with a temperature typically in the interval 850- 1050°C, in which the energy content of the flue gases is utilized. Then, the flue gases are conducted further with a lower temperature of typically 180-250°C to the flue-gas cleaner L, in which εolid particles and posεibly other εubstances are filtered out of the flue gases, after which the latter are transported further by means of the fan M to the chimney N and discharged to atmos¬ phere. Out of consideration to the environment it is desirable that the substances being discharged in the form of slag and flue gases are as environmentally neutral as posεible. With regard to the slag, this meanε that i.a. organic substances are either incinerated or sterilized to kill contaminating bacteria and germε, and that the content of heavy-metal compounds and other substances is as low as possible, which conditions are best achieved by meanε of an effective uniform incineration. With regard to the flue gas, it is likewise beεt ensured that the content of i.a. dioxines, carbon monoxide and NOx iε as low aε possible by means of an effective uniform incineration.
Figure 2 showε the grate system in the combustion chamber F. This grate system may be divided into an infeed grate R and four succeeding grates as shown in the drawing for conveying the waste through the proceεε of incineration. Thiε proceεε of incineration can typically be divided into four phases: I drying-out, II ignition, III combus- tion and IV burning-out, and the grate system may be divided into a greater or smaller number of grate sec¬ tions. The individual grate sectionε are conεtructed with travelling grates consisting of two sets of grate parts, of which at least one is movable as represented by the grate beam 1 in the grate section II, while the other grate parts may be stationary as represented by the grate beam 1 in the grate section I; the functioning of these travelling grates will be explained in more detail below.
At the beginning of the infeed grate R waste is introduced from a fuel chute (not εhown) . When the infeed grate R is "travelling", it withdraws waste from the bottom of the waste chute E and moves it forward and downward in the direction towards the right in the drawing. During this forward conveying, the waste is "torn open" by the infeed grate R so that it begins to distribute itself evenly over the infeed grate R, and is supplied with air from outside.
After having passed the infeed grate R, the waste is transferred to the grate section I and is supplied with additional air, air being conducted along and above the grate in section I and blown up through the grate from the primary-air chamber P, respectively. This treatment with air provides a continued drying-out of the moisture content in the waεte, aε already started on the infeed grate.
After having pasεed the grate in the grate section I, the waste is transferred to the grate in the grate section II. In this section, the waste is conveyed further in the forward direction, during which the temperature in- creaεes, so that ignition of the waste is started, if εuch ignition has not already occurred on the infeed grate or in the grate εection I. During this conveying, the tearing-open of the waste by the grate is continued.
After having pasεed grate εection II, the waεte, now having been ignited, is tranεferred to grate εection III; this is where the incineration as such occurs, during which the major part of the energy in the waste is libe¬ rated.
After the incineration on the grate sectionε I+II+III, the waεte is transferred to the burning-out section IV, on which combustible residue iε burned out. After having paεεed through the grate εection IV, the waεte, now being completely burnt-out, is discharged in the form of slag in the slag chute S.
Figure 3 shows a movable grate beam 1 corresponding to the one shown in grate section II in Figure 2. On this grate beam, grate blocks 3 adapted to be in contact with the waste, are placed. This grate beam is assembled to¬ gether with a number of grate beams extending parallel to it, so aε to form a grate. In the interεpaces of the grate, a second grate or grate part iε placed, e.g. in the form of a stationary grate like the one shown in grate section I in Figure 2. The movable grate shown in Figure 3 executes upward and forward progressing pendular movements produced by supporting the grate beam 1 on the periphery of a shaft in the recess 7. The other end of the grate beam 1 is movably supported through a footpiece 13, allowing the grate beam to execute reciprocating movements, also allowing thermal expansion in itε longi¬ tudinal direction. In operation, the movable grate will, through itε upward and forward progreεεing wave movement, move forward from the plane formed by the second grate and lift the waste and convey it forward through a short diεtance. After thiε, the movable grate will deεcend below the plane formed by the εecond grate, εo that the waεte will be εupported by the latter, and then, the movable grate will execute a downward and rearward wave movement, after which the procedure iε repeated. During the εtepwiεe progressing conveying, the waste resting on the grate will alternately be lifted and lowered.
The alternate lifting and lowering of the grate and the waεte referred to above will transfer large pulsating loads to the εupportε for the grate, and in the previouεly known technology, the primary purpose of the means sup- porting the grate has been to support the grate without transmitting vibrations to the surrounding structural parts. Thus, in the previously known technology, the supporting means are primarily constructed with a view to creating a secure foundation.
By using a travelling grate with two movable grate partε, e.g. in the manner known from Daniεh Patent Application No. 647/94, it is posεible to achieve a conveying creating leεε vibrations. Figure 4 shows the drive mechanism for the grate beams in such a doubly-movable grate. In this arrangement, a first grate beam 1 belonging to a first grate part iε εupported by a firεt εhaft 9 through a first carrier 11 in the recess 7, whereas the second grate beam 2 belonging to the second grate part is sup¬ ported by a second shaft 10 through a second carrier 12 in a recess 8. When these two shafts 9 and 10 are driven with pendular movements in counter-phase, the grate part comprising the grate beamε 1 and 2 will alternately exe- cute an upward and forward progressing movement, εo that the waεte will be conveyed alternately by the first grate part and the second grate part. With this arrangement, a more uniform conveying and lesε vibrations are achieved, i.a. because the lifting heights may be reduced to one- -half when the grate parts move in counter-phase.
In conventional incineration plants, in which such tra¬ velling grates are used for conveying the waste to and through the procesε of combuεtion, the travelling grateε are primarily conεtructed with a view to conveying the waεte and to be able to withstand the loads, to which they are subjected, as well as to tear-open and distribute the waste over the grate in order to facilitate the in¬ cineration and make it uniform. The travelling grates are εubjected to large mechanical loads, since they must be able to carry and lift all the waste resting upon them, and especially the travelling grate situated below the fuel chute and constituting the infeed grate R may be subjected to the total weight of the waste being pres¬ ent in the fuel chute.
The thermal influences alεo place great demandε on the fuel grates, especially the one situated in the combustion chamber. This grate must be able to accommodate the full longitudinal expansion caused by the thermal influence from a cold start to the full operational temperature.
The grates as such must be constructed so as to be able to tear-open the waste and distribute it over the grate in the optimum manner without the waεte getting stuck in the grate; such waste may e.g. consist of larger parts of furniture and fine dust as well as ashes. Further, the grates must be made of a material being able to with- stand the aggressive gaseε being produced during the proceεε of combustion in the best possible manner. At the same time, the movable parts muεt be constructed with a view to countering and resiεting wear cauεed by duεt and aεheε in the best possible manner. Thus, when designing the previously known grates for waste incinera¬ tion, the effort has been directed to providing arrange¬ ments, in the best posεible manner being able to withstand the loads, to which the travelling grate is subjected, and to function as a conveyor. With regard to control and monitoring, the only feature of the previously known travelling grates for waste incineration iε that of vari¬ able εpeed.
With the increaεingly εtrict demandε on the production of energy in the waεte-incineration process made by the combined power and heating stationε, as well as the de¬ mands to the combustion as such set by a uniform waste- incineration process, it is desirable to achieve further improvements in the process of combustion.
In order to achieve this in an improved manner in in¬ cineration plants, it is necesεary to provide additional control and monitoring of the combuεtion process.
The present invention is baεed upon the idea of including the infeed grate R and/or other grates in the form of travelling grates in the production of parameters by providing these grates with a weighing-cell arrangement and using the weight εignalε produced for deriving addi¬ tional parameterε for use in the control and monitoring.
For the reasons mentioned above, no attempts have been made previously to provide a weight measurement on tra- veiling grates in incineration plants. The present inven¬ tion has, however, shown that such weight measurements may be carried out on a travelling grate, and that these measurements can advantageously be used in the control and monitoring function.
In this connection, it is necesεary to be aware of the rule-of-thumb εaying that waεte material can εupport a combuεtion proceεε if it contains at least 25% combustible matter, this meaning that a completely burned-out slag being discharged to the slag chute may have a residual weight constituting from 0 to 75% of the weight of the mass of waste material being supplied, typically 25%. Further, the useful calorific value can vary considerably due to variations in the water content, and in this case a rule-of-thumb indicates that waste material with a water content of up to 50% can support a combustion pro¬ cess.
According to the present invention, the weight measure¬ ments are provided by supporting the travelling grate on weighing cells (also called load cells) . A preferred embodiment for providing such weighing arrangement in the form of weighing cells 20a, 20c & 20d is shown in Figure 5. The supporting structure, generally designated U, supports a doubly moving travelling grate having grate beams 1, 2 of the kind shown in Figure 3, and is provided with drive arrangements 7-12 as shown in Figure 4. In this embodiment, the drive shafts 9, 10 are supported in the supporting structure U in flange bearings 15, 16, and the footpieces 13 are supported on a supporting beam 14, in the drawing being shown with an H-shaped profile. In the vertical direction, the supporting beam 14 is supported on the weighing cells 20a and 20b, as alεo shown in front view in Figure 6. The supporting beam 14 is only εupported in the vertical direction by the weigh¬ ing cells 20a-20d, while in the other directions, it is guided by guides 18, the latter by means of eye links allowing movement in the vertical direction only. The guide 18 at one end of the beam 14 prevents that end from moving in the longitudinal direction of the beam, while the guide 18 at the other end allows a certain longitudinal displacement of the beam so aε to accommodate thermal expansion of the latter. In the downward direc- tion, the weighing cells are supported on brackets 19a and 19b, the latter being supported below. This construc¬ tion with a supporting beam 14 supported in the vertical direction at both ends through respective weighing cells 20a, 20b and guided by a guide 18 solely allowing vertical movementε at one end of the εupporting beam 14, in the other end having a certain clearance in the longitudinal direction of the supporting beam 14 for accommodating thermal expansion, is especially well-εuited for producing weight εignals for weight distributions susceptible to variations transverεely of the travelling grate. With thiε weighing arrangement, each and every force exerted in the vertical direction on the beam 14 will be measured correctly as the sum of the weight signals from the two weighing cells 20a, 20b. Further, the guides 18 allow thermal expansion to be accommodated at the measuring device. With the guides 18 shown, it is, however, possible to increase the extent of the supporting beam 14 in the vertical direction with a view to shielding the weighing cells from the influence of heat from above, without compromising the capacity of the guideε 18 to guide the supporting beam 14.
In the other end of the supporting structure U, the εhaftε 9, 10 in the driving arrangement are εupported in flange bearings 15, 16, the latter being εupported vertically on four weighing cells, of which only the two, 20c, 20d on one side, are εhown. Thiε construction is especially well-suited for operation with vertical loads moving longitudinally and tranεverεely of the travelling grateε, εuch aε is the caεe with the driving arrangement for a doubly movable travelling grate as εhown. In this embodi¬ ment, the flange bearings 15, 16 are supported on the side wall 17, the latter transferring the forceε down- wardly to bracketε 25, that may have a εimilar shape as the brackets 19a, 19b in the weighing arrangement de¬ εcribed above. The bracketε 25 are secured to reinforce¬ ments 27 on the side wall 17. From the brackets 25, the vertical forces are transferred to the weighing cells 20c, 20d, a similar arrangement being present on the other side (not shown) . Downwardly, the weighing cells 20c, 20d are supported on columns 21, 22 with H-shaped profiles. In thiε embodiment, the function of guiding the side wall 17 and the bracket 25 is provided by the reinforcement 27 and other reinforcements (not shown) on the side wall 17. At one of its ends, the reinforcement 27 is connected to a guide 24 preventing movement of the reinforcement 27 in its longitudinal direction and with a guide 23 situated above the guide 24 at the upper part of the side wall 17, in this location allowing vertical movements but at the same time preventing the εide wall 17 from moving in directions at right angles to the plane of the drawing. An additional guide 23 situated oppositely on the upper side of the side wallε 17 allows a certain movement in the vertical and longitudinal directions. Altogether, the guides 23, 24 allow thermal movements of the side wall 17 with the reinforcements 27, at the same time as the vertical forces are restricted to being ex- erted upon the weighing cells 20c, 20d. A similar arrange¬ ment exists on the other side (not shown) of the sup¬ porting structure U. Thus, this embodiment will comprise a total of four weighing cells, of which only the two designated 20c and 20d are visible in Figure 5, making it poεεible to obtain correct measurements of forceε moving in two dimensions, because the sum total of the weighing signals from the four weighing cells will always repreεent the correct value for the total load. It is also possible to produce the weighing signals by using three weighing cells, but this simplification of the weighing cells would produce a more complicated εupporting arrangement than that achieved in a εimple manner by uεing the εide walls 17. With the embodiments shown, it is posεible to achieve a correct weighing of a load moving in one and two dimen¬ sions, respectively, at right angles to the vertical.
A person skilled in this art will, of course, be able to construct guides capable of transferring the vertical forces correctly to a single weighing cell. This will, however, make the guides more complicated when at the same time account is to be taken of thermal expansion and contamination from falling particles.
A travelling grate being uεed aε an infeed grate R in incineration plantε and being provided with one or a number of weighing cellε placed at one end or both endε can advantageouεly be used at a number of locations in the infeed-grate line in a waste-incineration plant.
Aε an example, an infeed grate R provided with one or a number of weighing cellε 20 in the end cloεeεt to the infeed of waεte can produce a weight signal being mainly a function of the force exerted on the grate R by the waste being preεent in the fuel chute E. This weight signal can at an early moment in time give a warning about bridge formation or other blockage in the fuel chute beginning to take place, because such a blockage will cause the weight εignal being produced to show a decrease without a simultaneous reduction of the height of the filling in the fuel chute E. Thus, it will be posεible to take remedial action with a view to breaking the blockage before the latter can be interpreted aε a lack in the supply of waste to the infeed grate R.
Thiε weight εignal can also be used to provide information about the consistency of the waste, becauεe the volume of the waste in the fuel chute E can be computed on the basis of the geometry of the fuel chute and the filling height of the fuel in the fuel chute E. When, in addition to knowledge about the volume, information about the weight is provided, it is poεεible to calculate the aver¬ age specific weight. This information about the specific weight can be used to make an estimate of the mass of waste being advanced by the infeed grate R at a given speed. The specific weight can also be used to make an estimate of the water content in the waste. This can e.g. take place in connection with a visual inspection, in which the waste in general has been identified; e.g. cardboard will have a specific weight that is proportional to the water content. This specific weight will at the same time increaεe in the fuel chute E, becauεe moist cardboard is more eaεily deformable than dry cardboard and has a tendency to agglomerate, accentuated by the increased pressure exerted upon the lowermost material by the waste in the fuel chute E. This information can be used to lower the speed of the infeed grate R, because for a given speed of the infeed grate, the masε of waεte being εupplied is greater than it would be with dry card¬ board. Since moist cardboard is more difficult to burn and at the same time has a tendency to agglomerate, this will also provide information that the maximum allowable flow-through εpeed for the waste through the combustion zone is lesε than for dry cardboard, becauεe otherwise, there would be a risk of un-burned material existing within lumps not having been torn open during the con- veying on the infeed grate. It is alεo possible to use this information to control the amount and temperature of the air supplied for drying and combuεtion.
If the infeed grate R is also provided with at leaεt one weighing cell 20 in the downεtream end, thiε weight εignal may be used to provide a better estimate of the mass flow of waste on the infeed grate R. Further, this signal may be used to give an early warning that waεte haε got stuck on the infeed grate R, since waste getting stuck in the infeed grate R will produce a blockage of the subsequently arriving waste and thuε cause waste to ac¬ cumulate on the infeed grate R upstream of the place at which the waste haε become εtuck. A sign of this situation iε that the distribution of weight on the infeed grate R is displaced in a direction opposite the conveying direc¬ tion without it being posεible to relate thiε weight- diεtribution diεplacement to the infeed of waεte.
Since the height or area in the vertical direction of the waεte material being unloaded below the infeed arch or beam can be conεidered conεtant, the volume of unloaded waste will be known. This known volume can be used for computing the instantaneous specific weight of the waste when its weight iε measured by one or a number of weighing cellε 20 εituated downstream of the infeed arch or beam. If the weighing cell or cells is/are situated at a grate downεtream of the infeed grate R and the infeed arch or beam and are being driven with a different εpeed, the volume will, of courεe, be corrected inverεely proportio¬ nal to the εpeed ratio.
Thuε, it iε possible to provide specific-weight computa¬ tions for the waεte at any time being supplied for in- cineration, which is very useful.
If further, the succeeding grateε are provided with weigh¬ ing cellε, the latter can - in addition to providing alarm εignalε about infeed problemε - provide information about the procesε of combuεtion, eεpecially the reduction in weight occurring through drying-out and combuεtion, reεpectively. Thiε information can e.g. be used for deter¬ mining the maximum speed of the infeed grate R and/or the remaining grates. This maximum speed may e.g. be divided into two levels, one level being a maximum normal operating speed and the other being a maximum peak-load speed. The maximum normal operating speed may be deter¬ mined on the condition that no subεtantial reduction of weight in the waste must occur during the burning-out in the grate section IV. This may be achieved by the control and monitoring unit εignalling to the operator that he iε free to control according to other parameterε, εince the incineration of the waste takes place safely and completely. The maximum peak-load speed may be determined on the condition that the reduction of weight during the burning-out in the grate section IV must not exceed a value forming a certain ratio with the reduction of weight occurring during the combustion in the grate section III. Thuε, the reduction of weight during the burning- out may e.g. be set to 20% of the reduction in weight occurring during the combustion. Thiε may e.g. be achieved by the reduction in weight being computed from weight signals from the inlet and outlet end of the individual grate, and the reduction of weight during the combustion proceεε is related to the reduction in weight during the burning-out procesε. When the ratio of weight reduction during the burning-out to that during the combuεtion iε below a certain value, the control function or the oper- ator iε free with regard to excercising control according to other parameters, but if this value iε reached, the weight εignalε can be uεed to control the speed of the grates so as to maintain thiε ratio. In thiε caεe, the parameterε derived from the weight εignalε will take over the control of the speed of the infeed grate R, possibly also that of the succeeding grate, as well as the process of combustion, so that the weight signalε now constitute the primary control signals with regard to the combustion proceεs. The maximum speed for the grate syεtem can also be determined based on a desired reduction in weight of the waste from the feeding-in to the fuel chute E to the diεcharge through the slag chute S. If in this case, the data procesεing iε εynchronized with the εpeed of the infeed grate, it iε poεεible to follow the waste throughout the complete incineration proceεε, and any deviations can be regiεtered quickly. Thuε, e.g. large reductionε in weight from the feeding- -in to the termination of the combuεtion proceεε aε such can indicate a great proportion of combustible matter in the waεte, and the εpeed of the infeed grate can be reduced correspondingly. Converεely, a small reduction in weight may indicate a εmall proportion of combuεtible matter and/or matter that will not burn eaεily in the waεte, and this signalling can be used for immediately reducing the speed of the infeed grate and initiate the feeding-in of alternative fuel, e.g. in the form of gas or coal, with a view to maintaining the production of energy and at the same time retain a complete burning- out of the waste.
The following paragraph describes a hypothetical example of how the weight signals can be included in the control of the combustion process in a combined power and heating station, other control parameters being omitted for ease of understanding.
As a point of departure, the combustion procesε iε run under normal operating conditionε in which the energy content per masε unit of waste is taken to be constant. In this situation, the speed of the infeed grate R is controlled on the background of the weight signals and the calculated specific weight of the waste in the fuel chute E, εo that a constant masε flow of material iε delivered from the firεt infeed grate R. The succeeding grates are controlled with a speed, according to experi¬ ence providing optimum combustion. Becauεe after this, a period of peak load is expected to occur, the plant is slowly run up to the maximum normal operation speed for the grate system in the manner deεcribed above, with a view to achieving a εtable and uniform proceεε of combuε¬ tion and well-controlled thermal expansion in the plant. Then, when the period of peak load occurs, the combustion procesε will follow the inεtantaneouε energy demand, until the maximum peak-load εpeed for the infeed grate iε reached in the manner deεcribed above, after which the infeed of waste is maintained at this εpeed and addi¬ tional energy demand iε met by feeding-in alternative fuel or by letting another combined power and heating station take over the supply of energy. Aε will be evident from this example, the weight measurement according to the invention provideε εubstantially improved controlled parameters, that can advantageously be included in the parameters uεed for controlling the process of combustion and the supply of energy from a combined power and heating station using waste aε itε fuel.
The weight εignalε produced by the weighing cellε at the travelling grates are influenced by the vibrations occur¬ ring during the operation of the travelling grate, for which reason they must be filtered and/or averaged. This may advantageously occur in synchronism with the speed of the travelling grate, so that the time constants of a filter are varied in proportion to the cycle time (1/εpeed) of the travelling grate. With thiε arrangement it is achieved that when the dead time for producing the weight signals varieε proportionally with the εpeed, the points with which the weight signals are related will always be in the same location on the travelling grate.
In order to increase the εenεitivity of the weighing cellε at εmall loadε and at the same time retain the maximum measurable load, the weighing cell can be composed of a number of weighing cellε connected in εerieε, so as to make them function as if they were εtacked. With thiε arrangement, the most sensitive weighing cell in the series connection will produce the weight signals in a first, lowermost interval for loads, and when the limiting value for loadε in thiε first lowermost interval is ex¬ ceeded, the weight signals from the second most sensitive weighing cell are used, so that it is possible to achieve accurate measurementε at εmall loadε and still retain the maximum measurable load. The switching between the weight signalε from the various weighing cells in the series connection does, of course, not necessarily have to be carried out in the form of a complete switching at a certain limiting value, but may also be carried out gradually by varying the weighting of the signals from the individual weighing cells in the series connection.
LIST OF PARTS
A vehicle
B unloading silo
C crane
D feed hopper
E fuel chute/waste chute
F combustion chamber
I grate section
K boiler part
L flue-gas cleaner
M fan
N chimney
P primary-air chamber
R infeed grate
S slag chute
U supporting εtructure
I drying-out
II ignition
III combuεtion
IV burning-out
1 (firεt) grate beam
2 (εecond) grate beam
3 grate block
7 recess
8 recesε
9 firεt εhaft/drive shaft
10 second εhaft/drive shaft
11 first carrier
12 second carrier
13 footpiece 14 supporting beam
15 flange bearing
16 flange bearing
17 side wall 18 guide
19a bracket
19b bracket
20a weighing cell
20b weighing cell 20c weighing cell
20d weighing cell
21 column (with H-shaped profile)
22 column (with H-shaped profile)
23 guide 24 guide
25 bracket
27 reinforcement

Claims

1. Arrangement with a grate in an incineration plant, especially a waste-incineration plant, in which plant weighing of the fuel is carried out and at least one grate iε used for conveying fuel, especially waste, from a fuel supply (E) to a combustion space (F) , especially for use in plants uεing one or a number of grateε for conveying fuel through the combustion space (F) and fur- ther to the slag discharge (S) , said grate or grates being of the travelling-grate type and comprising at least one movable grate part (1) , characterized in that at least one travelling grate is εupported on at leaεt one weighing cell (20) capable of producing a εignal repreεenting the inεtantaneouε value of the weight, with which the weighing cell is loaded.
2. Arrangement with at least one grate according to claim 1, characterized in that the travelling grate being situated closeεt to the fuel εupply (E) , especially constituted by a fuel chute or εhaft (E) , is supported at the end closest to the fuel supply (E) by at least one weighing cell (20) .
3. Arrangement with at least one grate according to claim 1 or 2, characterized in that at least one tra¬ velling grate is supported at the end moεt remote from the fuel εupply (E) by at least one weighing cell (20) .
4. Arrangement with at least one grate according to claim 1, 2 or 3, characterized in that on at least one travelling grate, at least one end is supported by two weighing cells (20) .
5. Arrangement with at least one grate according to any one or any of the claims 1-4, characterized in that on at least one travelling grate, at leaεt one end, preferably the driven end, is supported by four weighing cells (20) , said travelling grate preferably being of the type having two movable grate parts operating in counter-phase.
6. Method for use in connection with an arrangement with a travelling grate according to any one or any of the claimε 1-5 in an incineration plant, eεpecially a waεte-incineration plant, in which at leaεt one grate is used for conveying fuel, especially waste, from a fuel supply (E) to a combustion space (F) , and especially in plantε uεing at leaεt one grate for conveying fuel through εaid combuεtion εpace (F) and further to the εlag dis¬ charge (S) , said grate or grates being of the travelling- grate type with at least one movable grate part, char¬ acterized in that the εignal from at least one weighing cell (20) being aεsociated with a travelling grate iε εupplied to a control and/or monitoring unit and uεed at leaεt for indicating an inεtantaneouε fuel-maεs value, especially relating to the maεε of waste being present on the travelling grate or grateε (R) concerned.
7. Method according to claim 6, characterized in that a weight εignal being produced by at leaεt one weigh¬ ing cell (20) in the vicinity of the fuel εupply (E) is used for monitoring the degree of filling of the buffer εtore conεtituted by the fuel supply (D, E) , preferably in the form of a fuel chute or shaft (E) .
8. Method according to claim 6 or 7, characterized in that the weight signal being produced by at leaεt one weighing cell (20) in the vicinity of the fuel εupply (D, E) constituted by a fuel chute or shaft (E) is used on the basis of knowledge of the geometry of the fuel chute or shaft and an indication of the height of filling of fuel, especially waste, in the fuel chute or εhaft (E) for computing the εpecific weight of the fuel, εaid filling height preferably being indicated continuously through automatic measurement, e.g. by means of ultraεonic or optical εenεorε or tranεducers.
9. Method according to any one or any of the claims 6- 8, characterized in that a weight signal being produced by at leaεt one weighing cell (20) εituated downεtream of the fuel chute or εhaft (E) , possibly being closer to the combustion space (F) , is used for monitoring the fuel mass in the combustion space and the process of combus¬ tion.
10. Method according to any one or any of the claims 6- 9, characterized in that the weight εignalε from at leaεt one weighing cell (20) iε/are uεed for monitoring the presence of irregularities and producing signalε indicating εame.
11. Method according to any one or any of the claimε 6-
10, characterized in that the weight εignalε from at leaεt one weighing cell (20) aεεociated with at least one grate are used for computing the masε flow.
12. Method according to any one or any of the claimε 6-
11, characterized in that the weight εignalε from at leaεt one weighing cell (20) associated with at least one grate are used for controlling the speed of the grate or grates.
13. Method according to any one or any of the claims 6- 12, characterized in that the weight signals from at least one weighing cell (20) associated with at least one grate are uεed for controlling the combustion process.
PCT/DK1996/000287 1995-06-27 1996-06-27 Arrangement with an infeed grate in an incineration plant, especially a waste-incineration plant, and method of using said arrangement WO1997001732A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
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Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DK0747/95 1995-06-27
DK74795 1995-06-27

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5546359A (en) * 1978-09-29 1980-04-01 Nippon Kokan Kk <Nkk> Incineration control method for city waste incineration
US5398623A (en) * 1992-05-13 1995-03-21 Noell Abfall- Und Energietechnik Gmbh Method for incinerating refuse, and a control process therefor

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5546359A (en) * 1978-09-29 1980-04-01 Nippon Kokan Kk <Nkk> Incineration control method for city waste incineration
US5398623A (en) * 1992-05-13 1995-03-21 Noell Abfall- Und Energietechnik Gmbh Method for incinerating refuse, and a control process therefor

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, Vol. 12, No. 282, M-726; & JP,A,63 058 012 (KUBOTA LTD), 12 March 1988. *
PATENT ABSTRACTS OF JAPAN, Vol. 14, No. 93, M-939; & JP,A,01 305 213 (KUBOTA LTD), 8 December 1989. *
PATENT ABSTRACTS OF JAPAN, Vol. 4, No. 88, M-17; & JP,A,55 046 359 (NIPPON KOKAN K.K.), 1 April 1980. *

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