METHOD AND INSTALLATION FOR HEAT RECOVERY IN FLUIDISED BED GRANULATION

Abstract

A process for producing granulated fertilizer by fluidized-bed granulation in a fluidized-bed granulator may involve drawing in and heating air used for fluidization in the fluidized bed via a conduit before entry into the fluidized-bed granulator. Hot exhaust air exiting the fluidized-bed granulator may be obtained, and a substream of the hot exhaust air may be recirculated and used for fluidization. Such recirculation creates the possibility of utilizing heat energy present in the exhaust air and decreasing heat energy necessary for heating the fresh air for fluidization. The recirculated air can be, for example, purified by way of a cyclone precipitator to separate off solid particles before the purified exhaust air is combined with the fresh air.

Claims

1.-22. (canceled)

23. A process for producing granulated fertilizer by fluidized-bed granulation in a fluidized-bed granulator, the process comprising: drawing in and heating air used for fluidization in a fluidized bed before the air enters the fluidized-bed granulator; obtaining heated exhaust air exiting the fluidized-bed granulator; and recirculating a substream of the heated exhaust air to heat the air that is drawn in and used for fluidization.

24. The process of claim 23 comprising mixing the substream of the heated exhaust air that is recirculated with the air that is drawn in to form mixed air that is used for fluidization.

25. The process of claim 23 comprising feeding the substream of the heated exhaust air that is recirculated and the air that is drawn in to a heat exchanger, wherein the heating of the air that is drawn in occurs at least partially in the heat exchanger via the substream of the heated exhaust air that is recirculated.

26. The process of claim 23 comprising at least one of partially mixing with the air that is drawn in or replacing the air that is drawn in by an exhaust gas stream from a plant; preheating the air that is drawn in via heat of a fluid stream that originates from a plant; or mixing exhaust gas streams from plants with the substream of the heated exhaust air that is recirculated in a conduit.

27. The process of claim 23 comprising: feeding the substream of the heated exhaust air that is recirculated and the air that is drawn in to a first heat exchanger where the air that is drawn in is heated by the substream of the heated exhaust air; and feeding the substream of the heated exhaust air that is recirculated and the air that is drawn in to a second heat exchanger where the air that is drawn in is heated by a source other than the substream of the heated exhaust air.

28. The process of claim 23 comprising heating the air that is drawn in by a source other than the sub stream of the heated exhaust air.

29. The process of claim 23 comprising heating the air that is drawn in with steam having a pressure up to 16 bar.

30. The process of claim 23 comprising heating the air that is drawn in with a fuel gas that heats a burner.

31. The process of claim 23 comprising purifying the air that is drawn in prior to feeding the air to the fluidized bed.

32. The process of claim 31 comprising causing the air that is drawn in to flow through a purification apparatus and/or a filter device before the air is fed to the fluidized bed.

33. The process of claim 31 comprising causing the air that is drawn in to flow through a first purification apparatus and a second purification apparatus before the air is fed to the fluidized bed.

34. The process of claim 31 comprising causing the air that is drawn in to flow through a cyclone precipitator as a purification apparatus before the air is fed to the fluidized bed.

35. The process of claim 31 comprising causing the air that is drawn in to flow through a cyclone precipitator as a first purification apparatus and then through a filter device as a second purification apparatus before feeding the air to the fluidized bed.

36. A plant for producing granulated fertilizer by fluidized-bed granulation, the plant comprising: a fluidized-bed granulator; a first conduit for feeding air for fluidization to the fluidized-bed granulator; a second conduit for feeding a solution containing substances for production of granulated material to the fluidized-bed granulator; a third conduit for discharging heated exhaust air from the fluidized-bed granulator; and a return conduit leading from the fluidized-bed granulator, wherein by way of the return conduit a substream of the heated exhaust air is configured to be recirculated into the first conduit.

37. The plant of claim 36 comprising a purification apparatus disposed in a flow path of the return conduit between the fluidized-bed granulator and the first conduit.

38. The plant of claim 36 comprising a blower disposed in a flow path of the return conduit.

39. The plant of claim 36 comprising an air heater disposed in the first conduit, wherein the return conduit opens into the first conduit upstream of the air heater.

40. The plant of claim 36 comprising a fresh air blower disposed in the first conduit upstream of a junction with the return conduit.

41. The plant of claim 36 comprising: a separate conduit for a non-recirculated portion of the heated exhaust air, the separate conduit extending out from the fluidized-bed granulator; and a sucking exhaust air blower disposed in the separate conduit.

42. The plant of claim 41 comprising a purification stage disposed in the separate conduit for purifying the heated exhaust air to be discharged.

43. A process for producing granulated fertilizer by fluidized-bed granulation in a fluidized-bed granulator, the process comprising: drawing in and heating fluid for fluidization in a fluidized bed before the fluid enters into the fluidized-bed granulator; and at least one of the fluid originates from an exhaust gas stream of a plant, air drawn in for fluidization in the fluidized bed is at least partly mixed with an exhaust gas stream of a plant, or a part of an exhaust gas and/or a fluid stream from a plant is used for indirect preheating of the fluid for fluidization.

Description

[0049] A working example of the present invention will be explained in more detail below with reference to FIG. 1. Here:

[0050] FIG. 1 shows a flow diagram of an illustrative granulation plant for producing granulated fertilizer with heat recovery according to the present invention.

[0051] In the following, a possible working example of the present invention will be explained in more detail with reference to FIG. 1. The depiction shows a flow diagram of an illustrative granulation plant which is used for producing granulated fertilizer according to the invention. This plant is a type of plant which is designed, in particular, for the production of relatively small amounts of granulated fertilizer. A fluidized-bed granulator 17 is used for producing the granulated material. In this plant, the air used for fluidization is drawn in from the surroundings by a blower 23 and flows via the conduit 18 and through an inflow plate 2 into the process chamber 1. Before entry into the process chamber, the air passes through electric air heaters 10a, 10b. Spray nozzles 3 which are installed in the bottom spray configuration and spray the solution vertically upwards in cocurrent with the fluidizing air are located in the process chamber 1. The spray nozzles 3 are supplied via the conduit 20 with compressed air used as atomizing air.

[0052] The spray solution can be prepared batchwise in containers 8. Granulation additives can be dissolved in a first container 8a or be placed in the container as solution. The granulation additives are introduced via a conduit 11 into this first container 8a. Water for adjusting the concentration can be introduced via a further conduit 12 into this first container 8a.

[0053] The ammonium sulfate solution is prepared in a second container 8b. Water is firstly fed via a branched conduit 13 connected to the conduit 12 into this second container 8b and the ammonium sulfate (AS) is introduced as solution or more rarely in crystal form via a further conduit 14 into the second container 8b. The appropriate amount of additive solution is subsequently metered from the first container 8a into the second container 8b containing the AS solution. In some cases, the additive can also be introduced in crystal form into the AS solution. The solution is homogenized by means of a stirrer and preheated to the process temperature by means of a heating device. The solution is then conveyed by means of a pump 5 through the conduit 19 into the fluidized-bed granulator 17 at the nozzles 3.

[0054] Above the process chamber 1, there is an expansion chamber 4 which has a greater apparatus cross section than the process chamber 1. As a result of the increased cross section, the air velocity is reduced and discharge of the small particles from the system is reduced in this way. The exhaust air goes into an external purification unit 6 and is there freed of particles which have been discharged from the granulator 17. A blower 7 is located downstream of the purification stage, so that the entire plant is operated in suction mode (subatmospheric pressure). The granulated material taken off is classified by means of a sieve plant 9 into the three fractions oversize, product and undersize. The undersize material sieved off (fines) is recirculated via the conduits 15, 16 and introduced together with additional nucleus material into the granulator.

[0055] According to the invention, only a purified substream of the exhaust air is optionally discharged via conduit 26 from the system, while a further substream is recirculated in order to utilize the heat energy present in the exhaust air. For this purpose, a branch is provided in the exhaust air conduit leaving the granulator 17, so that this substream to be recirculated can be conveyed via the conduit pointing to the left in the drawing to a purification apparatus 21, which is, for example, a cyclone precipitator by means of which solid particles can be precipitated from the exhaust air stream. The solids particles separated off there can, for example, be conveyed via conduit 28 back to the container 8b in which the preparation of the granulation solution is carried out. A substream of the recirculated exhaust air purified in this cyclone precipitator 21 is then conveyed via a conduit 27 and a blower 22 into the conduit 18 via which the air for fluidization goes into the process chamber 1, with the introduction of the recirculated exhaust air preferably occurring downstream of the fresh air blower 23 and air heater 10a and upstream of the air heater 10b. The advantage of the use of the recirculated exhaust air is that heat energy is still stored in this, so that after combining with the fresh air which is fed in from the outside and has been partially heated in the air heater 10a downstream of the blower 23, further heating of the introduced fresh air by the hot exhaust air occurs. As a result, the energy required for heating the total air for fluidization by means of the air heater 10b is reduced.

[0056] At the same time, the streams 18 and 26 are decreased by recirculation of a substream. As a result, the requirements having to be met and the power uptakes of the blowers 7 and 23 and also the purification unit 6 are reduced.

[0057] FIG. 2 shows an alternative embodiment in which, as an alternative to or in addition to the drawn-in fresh air, hot, suitable exhaust gas streams 30 from other (sub)plants are mixed with the recirculated stream in conduit 27.

LIST OF REFERENCE NUMERALS

[0058] 1 Process chamber

[0059] 2 Inflow plate

[0060] 3 Spray nozzles

[0061] 4 Expansion chamber

[0062] 5 Pump

[0063] 6 Purification unit

[0064] 7 Exhaust air blower

[0065] 8a First container

[0066] 8b Second container

[0067] 9 Sieving

[0068] 10a Air heater or heat exchanger stage 1

[0069] 10b Air heater or heat exchanger stage 2

[0070] 11 Conduit for addition of the additives

[0071] 12 Conduit for addition of water

[0072] 13 Conduit for addition of water

[0073] 14 Conduit for addition of the ammonium sulfate

[0074] 15 Conduit for recirculation of the fines

[0075] 16 Conduit for recirculation of the fines

[0076] 17 Granulator

[0077] 18 Conduit for fresh air

[0078] 19 Conduit for introduction of solution into the granulator

[0079] 20 Conduit for compressed air

[0080] 21 Purification of the recirculated air (cyclone)

[0081] 22 Blower for recirculated air

[0082] 23 Fresh air blower

[0083] 24 Conduit for coarse particles (to the crusher)

[0084] 25 Conduit for granulated product

[0085] 26 Conduit for purified exhaust air

[0086] 27 Conduit for recirculated air

[0087] 28 Conduit for separated-off solid particles

[0088] 29 Conduit for separated-off solid particles

[0089] 30 Conduit for exhaust gas stream from other (sub)plants