System of transporting combustion residues produced in a calciner

Abstract

System (100) of dry transport of solid combustion residues produced in a calciner (1005), which system (100) includes: - a dry transport assembly (1), itself comprising a belt conveyor (10) and a gas-tight and / or dust-tight casing (11); - connection means (2) to the bottom of a combustion air duct (1006) of the calciner, configured to allow continuous unloading of solid combustion residues; - adduction means (112) of cooling and post-combustion air (A4) in countercurrent on the transport assembly (1).

Description

[0001] SYSTEM OF TRANSPORTING COMBUSTION RESIDUES PRODUCED IN A CALCINER DESCRIPTION

[0002] Technical field of the invention

[0003] The present invention relates primarily to a system, or plant, of extraction and transport of solid combustion residues, including dust, produced in a calciner, particularly a precalciner, for example in cement production plants. The invention also provides an associated method of treating such residues.

[0004] Background

[0005] As is well known, the basic component for the production of cement, particularly so- called Portland cement, is clinker. The latter is typically obtained by a so-called calcination process, which is the dissociation of calcium carbonate (CaCOa) into calcium oxide (CaO) and CO2. Such process is carried out at a high temperature, typically above 850°C, in a so-called calciner ("calciner"). The latter typically includes a rotary kiln in which the base, i.e. , "raw," material is fed to be heated to obtain, precisely, clinker.

[0006] The diagram in Figure 1 shows an example of (part of) a clinker production plant of a per se known type. It includes the aforementioned rotary furnace, denoted 1000, which unloading the clinker C produced into a cooler 1001. In the latter, the clinker is treated by an inlet air stream A, with exhausted air discharged through an outlet duct 1003 or similar means.

[0007] The material in the furnace 1000 is heated by the combustion of a combustible F, together with a flow of combustion air A1.

[0008] The raw material M to be processed is fed into the furnace through a preheater 1004, such as a cyclone type and presenting a plurality of stages.

[0009] The plant also provides for an additional calciner, or precalciner, 1005 arranged upstream of calciner 1000 to perform preheating and / or heat treatment of M material. Such a precalciner 1005 provides its own combustion chamber arranged between the rotary furnace 1000 and the preheater 1004, which is fed by means of an input of auxiliary combustible F1, the latter being of the same or different type than combustible F. The combustion chamber of the precalciner uses as combustion air the hot gases A3 coming from the clinker cooler 1001, i.e., so-called secondary or tertiary air. This air is adducted to the precalciner 1005 by means of a so-called tertiary duct 1006. Onentering the rotary furnace 1000 the so-called "raw meal," i.e., preheated material M, thus has a temperature of about 850-900°C and is almost completely calcined.

[0010] At the bottom of the duct 1006 - and particularly at one or more elbow bends of it - solid combustion residues may be deposited. This is particularly the case for the coarser particles generated by combustion and, more generally, for all those particles that are not supported and entrained by the gas flow in the tertiary air duct. This problem is accentuated when alternative combustibles such as RDF (Refused Derived Fuel), TDF (Tire Derived Fuel) and / or biomass are used in the precalciner.

[0011] Under typical design conditions, the material to be removed results at high temperatures, around 850-900°C and above, and with particle sizes ranging from fine to about 250-300 mm maximum linear size. In terms of average flow rate in the hour, the amount of residue is generally around 3 tons or so under normal conditions and 5 tons or so as a peak value.

[0012] Currently, removal of solid combustion residues and clinker particles entrained by tertiary air deposited in the duct is generally done by ground unloading and removal by mechanical shovel or devices of similar function. The materials thus recovered, after cooling, are sent to landfill. The removal cycles of the aforementioned residues are carried out in "batch" mode, i.e., discontinuous. The interval between one unloading and the next varies depending on the quantities being deposited in the pipeline. The unloading may result in the need for plant shutdown.

[0013] Similar needs may occur in an adduction duct of combustion air to an intermediate or primary calciner.

[0014] The discontinuous nature of said material removal and the need to stop the plant are major drawbacks of known systems that lower their production efficiency and can complicate process automation. In addition, the current arrangements necessarily result in ash being dispersed into the environment. This does not completely guarantee the safety of operators and results in a dispersion of the thermal content of the ash itself.

[0015] Summary of the invention

[0016] The technical problem posed and solved by the present invention is therefore to provide a system of extraction and transport of solid combustion residues, including dust, from an adduction duct of air to a calciner, particularly a precalciner, which makes it possible to overcome the above-mentioned drawbacks with reference to the known technique.Such problem is solved by an extraction system according to claim 1 and a method according to claim 8.

[0017] Preferred features of the present invention are the subject of dependent claims.

[0018] The system of the invention provides for the mechanical transport, advantageously dry, of solid combustion residues produced in a calciner or precalciner and clinker particles entrained by combustion air, particularly so-called secondary or tertiary air. This is achieved by one or more belt conveyors, each preferably completely enclosed in a casing, which is gas-tight, in particular with respect to air, and / or dust-tight. The closed configuration of the system makes it possible to prevent the uncontrolled re-entry air, for example by the use of specific sealing means, such as double clapet valves.

[0019] The above conveyor may be of the belt type and possibly associated with collection means to collect the fines from the bottom of the casing. Such collection means consist, for example, of recovery chains or pendulum or spoon systems hinged to the belt.

[0020] The system may also include sieving means, such as dimensional or weight type, and / or provide for recirculation of materials at the head of the rotary kiln

[0021] A crushing stage for size reduction may be provided upstream or downstream of the sieving means.

[0022] The invention avoids a dispersion of dust into the environment, allowing for environmentally safe operation. It also allows for operator safety and a recovery of heat as enthalpy of the waste to be transported.

[0023] In addition, the continuous transport system for the above materials can allow for afterburning on the conveyor, which allows for the recovery of chemical energy provided by the conversion of carbonaceous residues and / or sensible heat derived from the cooling of the transported residues.

[0024] As mentioned above, the system of the invention includes at least one belt conveyor of high-temperature bulk solids, which can be realized, for example, according to the teachings of WO2011 / 036587A2 or WO2014 / 013472.

[0025] Other advantages, features, and ways of using the present invention will be evident from the following detailed description of some embodiments, presented for illustrative and non-limiting purposes.Brief description of the figures

[0026] Reference will be made to the figures in the attached drawings, wherein:

[0027] ■ Figure 1, already introduced above, shows a general scheme of possible configuration of a calcination plant of known type;

[0028] ■ Figure 2, shows a schematic representation, in a side view, of a system of extraction and transport according to a preferred embodiment of the present invention;

[0029] ■ Figure 3 shows a perspective view of part of a belt conveyor that can be used in the system in Figure 2, according to a preferred embodiment of it;

[0030] ■ Figure 3A shows an enlarged detail of Figure 3.

[0031] The invention applies to any calcination plant configuration, and / or precalcination, possibly other than that exemplified in Figure 1.

[0032] Detailed description of preferred embodiments

[0033] Various embodiments and variants of the invention will be described below, with reference to the figures introduced above.

[0034] Similar components are denoted in the different figures with the same numerical reference.

[0035] In the detailed description that follows, additional embodiments and variations with respect to the embodiments and variations already discussed in the description will be illustrated only insofar as they differ from what has already been stated.

[0036] In addition, the different embodiments and variations described below are likely to be used in combination where compatible.

[0037] With reference to Figure 2, a system, or plant, of extraction and transport of solid combustion residues, including dust, is denoted overall with 100. The system 100 is associated with or associable with an adduction duct of air to a calciner or precalciner, such a duct being also in Figure 2 denoted with 1006. The air flow in the duct, typically so-called tertiary air, is represented by dashed lines and arrows and denoted with A3.

[0038] The system 100 comprises a mechanical transport assembly, advantageously dry anddenoted overall by 1. The transport assembly 1 comprises a sealed casing 11, preferably metallic, enclosing a conveyor 10, for example a belt type.

[0039] The belt conveyor 10 comprises a continuous, mobile, high-temperature resistant conveyor belt, which in this example has a closed loop configuration. The conveyor 10 has, in use, a forward section 101 for transporting the material, according to a transport longitudinal direction indicated by arrows R, and a return section 102 that moves in the opposite direction. The belt wraps around two elements, specifically a motor drum 103 and a return drum 104 respectively, defining the aforementioned closed loop configuration.

[0040] An initial section of conveyor 10 defines a loading region 110 of material arranged at the bottom of the duct 1006 from which residual materials are extracted. In a typical operative mode, during a forward stroke the conveyor transports such material, in essentially continuous bed form, to its own movable conveying surface corresponding to the top of the belt stroke and also denoted 101. The forward direction of the conveying surface is the longitudinal direction of the belt and denoted by way of example with arrows R.

[0041] It is also possible to provide for discontinuous operation of the system.

[0042] As shown in more detail in Figures 3 and 3A, in the present example realization, the belt is of the type comprising a mesh element 105, preferably metallic, which supports a plurality of adjacent or partially overlapping plates, one of which is denoted by way of example with 106. The plates 106 are thus moved integrally to the mesh element 105. The plates may have lateral fins or sides 107 to contain the material, extending longitudinally for the entire development of the belt. The assembly formed by the mesh 105 and the plates 106 can be supported on idle rollers 108, if necessary, both in the forward and return sections.

[0043] In a preferred embodiment, an automatic greasing device is provided for the aforementioned bearing and return rollers.

[0044] The plates 106 are able to support a bed of residual material to transport it along a predetermined path that basically corresponds to the upper horizontal travel of the belt, according to the arrows R in Figure 2.

[0045] Referring again to Figure 2, the system 100 then includes connecting means 2 between the transport assembly 1 and the duct 1006, which allow the extraction of residues deposited at the bottom of the duct itself, particularly at a sharp bend of it or other deviation. Such connection means 2 preferably comprise:

[0046] - a mechanical joint, preferably configured to compensate for thermal expansion ofboth the aforementioned duct 1006 and downstream components; and / or

[0047] • a shut-off valve, resistant to high temperatures and normally open, which closes in emergency conditions or when it is necessary to isolate the duct 1006 upstream from the system 100 located downstream.

[0048] The type of valve can be blade type, clapet or other.

[0049] In a complementary or alternative implementation, the valve may comprise a three-way diverter to provide an additional outlet for emergency discharge of transported materials, for example, if the system 100 is temporarily unavailable.

[0050] If there is no height space at duct 1006, it is possible to equip the duct with a dedicated emergency exit, denoted by 20 in Figure 2.

[0051] The transport assembly 1 is configured for the transport and cooling of solid bulk material, preferably with air, in particular ambient air. In one variant of the realization, the cooling is carried out mainly dry with air or another gas or fluid, but an emergency operating mode can be provided with the adduction of water or another fluid, or even exclusively. Such emergency water adduction means are shown schematically in Figure 2 and denoted therein by 13.

[0052] The cooling air within transport assembly 1 , specifically ambient air, is denoted by flow arrows A4 in Figure 2 and is drawn into the machine by the negative pressure (exemplified in the range of about 500-1000 Pa) that prevails in the tertiary air duct 1006. In the example shown, air is adducted within the casing 11 to lap the free surface of the material being transported via an inlet 112 associated with a valve 113. The air inlet 112 is arranged at a longitudinal end of the transport assembly 1 opposite the connection to the duct 1006, at or near an unloading region 111 of material.

[0053] Of course, a plurality of air inlets and possibly associated valves can be provided.

[0054] The inlet valve(s) of cooling air A4 are specially designed in number and size according to the above mentioned vacuum values within the upstream duct 1006. The valve or valves can be equipped with rotary actuators to adjust their opening position.

[0055] The transport assembly 1 may include means 15 for the recovery of fines from the bottom of the casing 11.

[0056] In the present example, such means 15 include a vertical bucket conveyor arranged at a longitudinal end upstream from the transport direction R, particularly upstream of the loading region 110 of material. Such means can be manufactured as described in WO2009 / 138949A1.The system 100 also comprises means 200 of adduction of cooling air, preheated, from the transport assembly 1 to the interior environment of the duct 1006. Such means include, in the present example, a bypass pipe and related accessories, particularly one or more sectioning valves. The flow of air tapped from the environment of the transport assembly 1 and fed into the duct is indicated by A4'. Such means 200 are arranged at an intermediate portion of the conveying surface, between the loading region 110 and the unloading region 111.

[0057] The system may also include one or more optical pyrometers, or other sensor or transducer means, for monitoring the temperature of materials being transported within the environment of transport assembly 1 defined by the casing 11.

[0058] A diverter 3, advantageously three-way, is provided at the exit of transport assembly 1 to load the transported material, alternatively, onto a sieving device 4 or a second transport assembly T of the same type already described.

[0059] The sieving device 4 can be based on size of particles, thus be of the dimensional type, and send particles that are smaller than the chosen threshold size to the machines located downstream. The oversized material, on the other hand, is conveyed to the aforementioned second assembly T.

[0060] The under-sieve material can be adducted to an additional transport assembly 5 that unloading it into the rotary furnace 1000.

[0061] The sieving device can also be of the weight type.

[0062] In the present example, the additional transport assembly 5 is a bucket elevator, which brings the material to a sufficient elevation for a gravity unloading into the furnace 1000.

[0063] In such a further transport assembly 5, the material may be further cooled by a flow of ambient air A5, preferably adduced countercurrent. Such air, or part of it, downstream of the crossing of the further transport assembly 5, may be adducted within the environment of the casing 11 of the transport assembly 1 , particularly at or near the unloading region of material. Such an inflow into transport assembly 1 is denoted by A6 in Figure 2.

[0064] The unloading of the additional transport assembly 5 may be associated with a sealing or isolating device 6 (so-called "air loc ') to keep the environments of the calciner and transport system 100 separate. This device 6 may include, for example, a double clapet valve, a pair of blade valves, or similar.At the exit of the second transport assembly T, the materials can be unloaded on the ground, for example in a box.

[0065] In correspondence with the unloaded material, a battery of water nozzles 7 can be provided to contain the dust, activated in a timed manner with the conveyor.

[0066] The system 100 may include one or more shut-off valves, normally open, to be operated in case of maintenance of upstream components.

[0067] According to preferred operative modes, the residual combustion materials, in particular those which pass through a grate of the calciner and flow into duct 1006, as well as possibly clinker particles entrained by the (tertiary) air flowing through duct 1006, are adducted into transport system 100 through connection means 2.

[0068] A post-combustion of such materials may develop on belt conveyor 10, particularly in the section immediately adjacent to the unloading of materials from duct 1006. Such post-combustion may be fed by the same cooling air A4 adduced within the environment of transport assembly 1.

[0069] The present invention has been described thus far with reference to preferred embodiment. It is to be understood that there may be other embodiments pertaining to the same inventive core, as defined by the scope of protection of the claims below.

Claims

CLAIMS1. System (100) of transporting solid combustion residues produced in a calciner (1005), which system (100) comprises:■ a continuous dry transport assembly (1 ), itself comprising:o a conveyor (10), particularly a belt conveyor, presenting a conveying surface (101) movable between a loading region (110) of the residues and an unloading region (111) of the residues and configured to transport the residues in the form of essentially a continuous bed, and o a gas-tight and / or dust-tight casing (11), enclosing said conveyor (10);Bconnection means (2) to the bottom of a combustion air duct (1006) of the calciner, configured to allow continuous unloading of solid combustion residues from the duct onto said transport surface (101);■ adduction means (112) of cooling and post-combustion air (A4) preferably countercurrent, at said conveying surface (101); and■ adduction means (200) of cooling air from said transport assembly (1) within the duct (1006) in the form of preheated air (A4’)_2. System (100) according to claim 1, wherein said connecting means (2) comprises a three-way diverter, configured to selectively communicate the duct (1006) with said transport assembly (1) or with an alternative discharge outlet.

3. System (100) according to claim 1 or 2, comprising, downstream of said unloading region (111) of said conveyor (10), a diverter (3) configured to selectively feed the transported residues to a second transport assembly (1') or to a sieving device (4), in particular of dimensional or weight type.

4. System (100) according to any of the preceding claims, comprising a crusher, preferably arranged upstream or downstream of a sieving device (4).

5. System (100) according to any of the preceding claims, comprising, downstream of said transport assembly (1), re-adduction means (5, 6) of the residues transported within a calcining furnace (1000).

6. System (100) according to any of the preceding claims, wherein said transport assembly (1) includes means (15) of recovering the fines from the bottom of said casing (11).

7. Cement production plant, which includes a transport system (100) according to any of the preceding claims.

8. Method of treating solid combustion residues produced in a calciner (1005), which method includes:* a continuous extraction of said residues from the bottom of a combustion air duct (1006) of the calciner; and° a dry mechanical transport of said residue on a conveyor (10), preferably a belt conveyor, in a selectively gas-tight and / or dust-tight environment, between a loading region (110) and an unloading region (111), wherein said residue are cooled on said conveyor (10) by an air flow (A4), preferably countercurrent, and wherein a post-combustion of said residue fed by said air flow (A4) is performed on said conveyor (10).

9. Method according to the preceding claim, wherein part (A4') of said air flow (A4) is adduced, in pre-heated form, within the combustion air duct (1006) of the calciner (1005).

10. Method according to claim 8 or 9, used in a cement production plant.

11. Method according to any of claims 8 to 10, which uses a system (100) according to any of claims 1 to 6.

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