FI85417C - A REQUIREMENTS FOR THE ADJUSTMENT OF TEMPERATURES IN A REACTOR WITH FLUIDISERAD BAEDD. - Google Patents

Description

8541 7

METHOD AND APPARATUS FOR CONTROLLING THE TEMPERATURE IN A FLUID LAYER REACTOR

RELEASE FOR THE ADJUSTMENT OF THE TEMPERATURE I AND REACTOR WITH FLUIDISERAD BÄDD

The present invention relates to a method for controlling the temperature in a fluidized bed reactor in which a circulating fluidized bed is formed by discharging some of the fluidized bed particles from the top of the reactor chamber, separating the gases in the particle separator and returning past the heat transfer surfaces in contact with them.

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The invention also relates to a circulating mass type fluidized bed reactor comprising a vertical reactor chamber with heat transfer surfaces arranged at the top. In a rotary-mass type reactor, a particle separator is connected to the upper end of the reactor chamber in addition to the flue gas traction, in order to separate the particles from the flue gas stream. Connected to the particle separator is a return pipe for returning the separated particles to the lower part of the reactor chamber and a degassing opening leading to the convection-20 part of the gases purified in the particle separator.

The fluidized bed particles are generally formed on the one hand from an inert bed material such as sand and ash, on the other hand from process feeds such as fuel and absorbents used e.g. for sulfur binding. The continuous circulation of particles in a circulating mass-type reactor considerably increases the residence time of the substances fed to the process in the process and thus improves, for example, combustion efficiency and sulfur binding. In addition, the high circulating mass has a smoothing effect on the temperature, as a result of which the temperature in the circulating fluidized bed is relatively uniform 2 8 5 41 7 throughout the reactor chamber and also over the entire particle cycle.

Indeed, most processes require that the temperature and gas flow be kept relatively constant in order to obtain optimal results from the fluidized bed reactor. In combustion processes, a temperature of about 850 ° C has proven to be advantageous for the whole. The temperature of 850 ° C is optimal for sulfur binding and high enough for combustion. At this relatively low temperature, the formation of nitrogen oxides 10 is negligible.

In a circulating fluidized bed type fluidized bed reactor, the particles fill essentially the entire reactor chamber, with the gas stream carrying the particles with it to the top of the chamber and from there on to the particle separator. The particles separated in the particle separator are returned to the lower part of the reactor chamber, from where they re-enter with the gas stream to the upper part of the chamber and from there on to the separator, thus continuing the circulation several times. With a given load, the heat transfer at the top of the reactor chamber can be controlled by the primary / secondary air ratio -20 la and the total mass of solids. The aim is to adjust the process so that the primary gas flow does not have to be varied within very large limits, despite load variations. The use of extra air is avoided. 25

The structure of the base plate is dimensioned so that the normal values of the primary currents give a suitable pressure drop across the base plate. The pressure drop must be sufficient to ensure even fluidization throughout the reactor chamber. Too low a pressure drop can cause uneven fluidization and even clogging of the air or gas nozzles. If the pressure drop is large, fluidizing the fluidized bed requires a lot of energy and becomes expensive.

35 Process temperatures must be kept constant despite load variations or, for example, when switching from one fuel to another. The temperature control measures must not adversely affect the circulating bed system of the circulating mass reactor.

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The temperature of the purified flue gas entering the convection section must also be maintained in such a way that, despite the load or fuel fluctuations, the convection section always provides sufficient power from the superheaters. In the superheater section, the temperature difference between the flue gas and the 5 vapors should be as large as possible. When firing with a small temperature difference, very large heat transfer surfaces have to be used.

As the load decreases, the convection section often no longer has enough power to superheat. Therefore, superheaters have often been added to the furnace of the actual fluidized bed reactor, at the top of the reactor, to obtain sufficient superheating power. However, hot superheater surfaces are susceptible to erosion under fluidized bed conditions. In addition, ash and other circulating material are sensitive to heat transfer tubes. In addition, the power of superheaters fitted to the furnace depends on variations in the temperature of the furnace, and it is difficult to guarantee a steady load-independent steam production with this solution.

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The thermal power from the fluidized bed reactor is partially adjusted automatically as a function of the load to correspond to the new load point. The heat transfer from the flue gases to the heating surfaces in the firebox takes place either as radiant heat transfer or as convection heat transfer. Convection heat transfer is highly dependent on the suspension density in the reactor. Heat transfer increases with increasing suspension density. By increasing the amount of primary air, the amount of circulating mass at the top of the reactor can be increased and thus the heat transfer to the heat transfer surfaces arranged in the top can be enhanced. However, increasing the total amount of air increases the amount of flue gases to be cleaned, i.e. increases costs. Increasing the primary air also increases the pressure drop across the base plate and thus also the energy consumption. A particular load 35 is generally associated with a certain total amount of air, so that it is better to influence the suspension density by adjusting the primary / secondary air ratio than by adjusting the total amount of air.

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The suspension density and thus the heat transfer at the top of the fluidized bed reactor has been proposed in Swedish patent publication SE 452359 to be adjusted by adding or reducing fine or coarse solids in the reactor. Coarse material 5 can be removed directly from the fluidized bed and fine material from the return pipe. Correspondingly, either coarse or fine material can be added to the reactor. By adjusting the ratio of fine to coarse material, the aim is to adjust the suspension density at the top of the reactor. 10 However, even at low loads from the top of the reactor, this method does not provide sufficient superheating power. According to the method, the suspension density at the top of the reactor is reduced at low load to maintain the optimum temperature. Changing the amount of material in the fluidized bed also causes problems such that with a small amount of material it is difficult to achieve uniform fluidization, and with a large amount of material, the pressure drop increases unreasonably.

Previously, for example, U.S. Pat. No. 4,312,301 and U.S. Pat. The circulating mass flow is then divided after the particle separator into two or more adjustable particle streams. One particle stream is returned directly to the reactor chamber. The other particle streams are passed to 30 external fluidized bed heat exchangers where heat is recovered by evaporators and superheaters.

In the solutions of the type mentioned above, the walls of the actual fluidized bed reactor are masonry structures or they are covered with a mass, whereby the temperature of the circulating mass leaving the reactor remains high. The aim has been to ensure that a sufficiently high heat output is obtained from the fluidized bed heat exchangers. However, the solution has not proved to be in line with expectations. Fluidized bed heat exchangers are large, separate plants and significantly increase plant costs and yet cannot guarantee the necessary thermal power for superheaters at a minimum load. With a minimum load in a circulating mass type fluidized bed reactor, the particle circulation remains very small. In this case, the efficiency of the separate heat exchangers operating on the fluidized bed principle also deteriorates in the absence of circulating mass. In addition, heat transfer surfaces in fluidized bed heat exchangers are highly susceptible to wear and are a real risk factor in the event of a possible steam or water pipe failure.

It is an object of the present invention to provide a method for controlling the temperature in a fluidized bed reactor which is better than the above.

It is a particular object of the invention to provide a method by which the temperature of the flue gases from the fluidized bed reactor, regardless of the load and fuel, can be adjusted to suit the superheat, while maintaining the chemically optimal temperature in the reactor. It is therefore an object of the invention to control the temperature of the flue gases in such a way that the flue gases, regardless of the load and the fuel, can be used for superheating after the particle separator 25.

It is a further object of the invention to provide a more flexible method for stepless temperature control of flue gases than known methods.

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It is also an object of the invention to provide a method for obtaining an adjustable thermal power from thermal surfaces arranged in a fluidized bed reactor.

It is also an object of the invention to provide a fluidized bed reactor in which the temperature of the flue gases in the actual reactor, regardless of the load and fuel, can be adjusted to suit the superheating.

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In order to achieve the above objects, the method according to the invention is characterized in that the passage of gases and subsequent particles is limited past the heating surfaces in different heat transfer zones at the top of the reactor 5 by adjusting the flow of gas - with a partition between the top of the reactor chamber with an orifice, at least 10 of which are adjustable, or - gas flow adjusting means fitted to or after the gas outlet of the particulate separators.

The fluidized bed reactor according to the invention is characterized in that - a partition wall is arranged in the flue gas draft of the fluidized bed reactor chamber, dividing the upper one which is adjustable and which connects the heat transfer zones to conduct flue gases from the first zone to the second zone, or that 25 to control the gas flows flowing through the gas outlets 30.

According to a preferred embodiment of the invention, the heat transfer zones are arranged so that the extension of the side wall of the reactor chamber forms a partition, and the second heat transfer zone is arranged in a horizontal plane next to the top of the reactor chamber. The upstream gas flow in the reactor chamber changes direction downstream after the septum.

7 S 5 41 7 Openings are arranged in the partition wall for directing gas from the first zone to the second. The flow of gas in the zones is controlled by adjusting the gas-5 paths in the partition, e.g. by enlarging or reducing the openings. By reducing some of the openings in the partition, the gas flow in some of the heat transfer zones is reduced at the same time. When the convection heat transfer is dependent on the gas velocity and dust density, the above-mentioned 10 control can reduce the heat transfer from the gas to the heating surfaces and the temperature of the flue gases is kept substantially constant.

For example, as the load decreases, the gas flow can be directed to pass mainly over the lower heat transfer surfaces 15, closing the openings in the upper part of the partition, and thus maintaining the flue gas temperature at the same level as at a higher load. Correspondingly, when the load rises again, the openings can be opened and the gas can also be directed over the upper heat transfer surfaces, whereby the temperature does not rise too much. The temperature of the reactor and the flue gases is thus controlled by adjusting the area of the total heat transfer surface bypassed by the gas flow.

By directing a larger or smaller portion of the gas flow through the upper or lower openings in the septum and thereby passing the gas flow either through the entire reactor chamber or only through the lower part of the reactor chamber, the effective height of the furnace is adjusted. With low load or poor fuel, the effective altitude can be calculated. 30 With full load and good fuel, the effective height can be increased.

With the reactor according to the invention, the temperature of the flue gases is controlled quickly and steplessly, completely or partially excluding part of the effective heating surface of the boiler. No separate heat exchangers are required to recover steam and heat.

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According to the invention, the walls of the fluidized bed reactor furnace can be formed from water pipe walls, whereby the actual furnace can be efficiently utilized in producing thermal power. The processes 5 in the fluidized bed reactor require a certain delay time, i.e. a certain reactor-chamber volume. In the solution according to the invention, the entire reactor chamber volume required by this process can be efficiently utilized to produce heat, and the walls do not necessarily have to be massed to limit heat transfer, as in previously known heat. In the compact fluidized bed reactor according to the invention, the temperature of the flue gases 15 is already adjusted in the furnace to suit superheating.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 schematically shows a fluidized bed reactor according to the invention in vertical section, Figures 2, 3 and 4 schematically show three other fluidized bed reactors according to the invention in vertical section and Figure 5 shows the reactor according to Figure 4 in cross-section.

Figure 1 shows a circulating mass type fluidized bed reactor 10 comprising a furnace or reactor chamber 12, a particle separator 14, a flue gas duct 16 from the top of the reactor chamber 30 to a separator and a particle return duct 18 from the separator to the bottom of the reactor chamber.

A wind cabinet 20 is arranged below the reactor chamber, which is connected to the reactor chamber 35 via a grate plate 22. Primary air or fluidizing gas is fed from the wind cabinet to the reactor chamber. The walls 26 of the lower part 24 of the furnace are masonry. The walls 28 of the reactor chamber are otherwise water tube walls 30.

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The upper part 32 of the reactor chamber is divided by a vertical partition 34 into two zones 36 and 38. The partition 34 forms an extension of the vertical wall 40 from the lower part of the reactor chamber. The partition wall has overlapping openings 42, 44 and 46, to which flaps 48, 50 and 52 are fitted, with which the open area of the openings can be reduced or with which the openings can be completely closed. The openings can be arranged laterally several times side by side, or the openings can be formed as narrow horizontal slots so that the flue gases can flow from one zone to another in the desired manner.

In addition to the water pipe walls, separate heat transfer surfaces 54 and 56 can be provided in the zones formed in the upper part of the reactor chamber. One or more heat surfaces can be arranged in the reactor chamber in each zone.

Separate vertical heat transfer surfaces may be arranged in the upper part of the reactor chamber in connection with the partition wall 20 so as to form separate substantially independent flow channels through which gases flow from the furnace to the other side of the partition wall. There is at least one opening in the partition wall for each flow channel. When part or at least one of the openings is adjustable, the flow channels can also act as heat transfer regulators. Closing the openings at one flow channel prevents the flow of gas in this channel and the transfer of heat from the channel to the heat transfer surfaces.

From the second zone 38, the flue gas duct 16 leads to a particle separator 14. In the embodiment shown in the figure, the separator is a horizontal cyclone with a degassing opening 58 arranged at one end. The gases are led through a degassing opening to a convection section not shown. The temperature of the flue gas in the reactor 35 according to the invention is substantially constant when entering the convection section, whereby sufficient power is always obtained from the superheaters arranged in the convection section.

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The particles separated in the separator flow from the cyclone to the return passage 18 and from there through the return opening 60 to the lower part of the furnace.

5 The firebox is further provided with fuel and other bed material supply means 62 and 64 and secondary air nozzles 66.

By adjusting the flaps 48-52, the flow of flue gas 10 can be controlled so that a greater or lesser portion of the flue gas flows through the openings 42-46. By directing a larger portion of the flue gases through the opening 46, the heat transfer from the flue gases to the heating surfaces, to the water pipe walls of the reactor top or to separate heating surfaces 54 and 56 is reduced.

As the load decreases, the temperature of the flue gases can thus be kept constant in the flue gas duct 16, 20 by closing the opening 42 and possibly the opening 44 as required and reducing the heat transfer from the flue gases to the upper heating surfaces. As the load increases, the heat transfer from the flue gases to the heating surfaces can be increased accordingly, by directing the flue gas into contact with the largest possible effective heating surface area. The heat transfer can be adjusted steplessly by reducing and enlarging the open area of the openings.

The gas flow can also be adjusted in the horizontal plane 30 so that the open area of the openings adjacent in the horizontal plane is reduced or increased in different proportions. In this case, vertical partitions can be arranged in connection with the apertured partition wall, which control the flow of gas in the vertical channels 35 perpendicular to it.

The open area of the openings in the partition wall can be reduced or increased, e.g. with a flap, as shown in Figs. 11 8541 7. The flap solution is simple and the flap does not have to be tight. However, the invention is not intended to be limited to a laptop solution. Other hot gas resistant solutions may also come into play.

5 The flaps can be individually adjustable or in groups. For example, all flaps in the same horizontal plane can be fitted to one shaft, so that they can be adjusted simultaneously. Correspondingly, if desired, the flaps on the same 10 vertical axes can be adjusted together.

The fluidized bed reactor shown in Figure 2 differs from the previous one mainly in terms of the particle separator 14. The particle separator is a so-called 15 a flow-through cyclone in which gas exits through a central tube 68 to a convection section, not shown. The separated particles flow from the bottom of the separator into the return pipe 18 and through the return opening 60 into the furnace. To facilitate the separation, a flow conduit 20, i.e. a drall former 69, is fitted to the flow-through cyclone, which provides a strong rotating flow to the cyclone.

In Fig. 3, a partition 34 with openings dividing the upper part 32 of the reactor chamber into two zones 36 and 38, 25 is arranged obliquely to the reactor chamber so as to divide the chamber into two overlapping zones. Below the partition wall are arranged vertical partition walls 70 and 72 formed of water pipe walls, which divide the zone 36 into different sub-zones 74, 76 and 78. By closing and opening the openings in the partition wall 34, the flow of flue gases to the lower zones can be controlled. When driving at low load or burning low quality fuel, the flue gases are mainly passed through the opening 46. At high loads and when burning high-quality 35 fuel, the flue gases are largely directed to pass through the opening 42 as well.

In the reactor according to Figure 3, the flue gases are led to a vertical cyclone separator comprising a separator chamber 80 and a degassing pipe 82. The separated particles are returned to the furnace via a return pipe 18. Various cyclone separators as well as e.g. ceramic filters are suitable for use in the fluidized bed reactor according to the invention.

In the embodiment shown in Figures 3, the flue gas draft is divided into lower zones on the furnace side of the partition wall. If necessary, the flue gas draft can also be divided into sub-zones on the partition wall on the side of the separator 10. In the reactor according to Figure 1, horizontal cooled partitions can be arranged perpendicular to the partition wall, which control the flow of the particulate gas.

Figures 4 and 5 show a reactor with the upper part connected to two adjacent cyclones 90 and 92. There is a partition 34 between the reactor chamber and the cyclones with openings 42 and 44. The openings have control flaps 48 and 50. The upper part of the reactor chamber is further provided with a partition 20 94 , which divides at the top into two channels 96 and 98 with heating surfaces, either on the walls of the channels or on separate heating surfaces. Of the channels, one 96 directs the flue gases to the first cyclone 90 and the other 98 directs the gases to the second cyclone 92. By adjusting the flap, the gas flow 25 at the top and thus the heat transfer can be affected.

In the embodiment shown in Figures 4 and 5, the gas flow can also be controlled by flaps 100 fitted to the degassing tubes 82, so that there is no need to fit flap openings between the top of the reactor chamber and the cyclones 30. In this case, the control flaps are adapted to a clean gas flow, which reduces the wear of the flaps. The control flaps can also be fitted to the colder parts of the gas duct if the gas ducts are divided into parallel parts.

The invention is not intended to be limited to the embodiments shown but can be modified and applied within the scope defined by the claims.

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Claims (24)

A method for controlling the temperature in a fluidized bed reactor in which a circulating fluidized bed is formed such that some of the 5 fluidized bed particles are discharged from the top of the reactor chamber, separated in at least one particle separator and returned to in contact with them, characterized in that the passage of gases and subsequent particles is limited past the heating surfaces in the different heat transfer zones at the top of the reactor by regulating the passage of gas through a partition wall fitted between the top of the reactor chamber and a particle separator. with gas flow control means fitted to or after the gas outlet of the particulate separators. 20 A method according to claim 1, characterized in that the direction of the gas flow is changed after the partition wall from upstream to downstream. A method according to claim 1, characterized in that the flow of the gas flow through the partition wall is controlled by adjusting the open area of the openings. A method according to claim 2, characterized in that the effective height of the reactor furnace is adjusted by directing the gas flow to pass through the lower or upper openings in the partition wall. A method according to claim 1, characterized in that the temperature of the gas fed from the reactor to the particle separator is controlled by adjusting the area of the total heat transfer surface bypassed by the gas flow. 14 8 5 41 7 A method according to claim 1, characterized in that the temperature of the fluidized bed is controlled by adjusting the area of the total heat transfer surface bypassed by the gas flow. 5 A circulating mass type fluidized bed reactor (10) comprising - a vertical reactor chamber (12) having heat transfer surfaces (30, 54, 56) arranged in the flue gas flow formed in the upper part (36), - at least one particle separator (14) connected to the flue gas flow , for separating particles from the gas stream, - a return pipe (18) fitted to the particle separator for returning particles from the particle separator to the lower part of the reactor chamber, and characterized in that a partition wall (34) is arranged in the flue gas outlet of the 20th reactor chamber, which divides the upper part of the reactor chamber into two heat transfer zones (36, 38), the first zone (36) being an extension of the reactor chamber and the second zone (38) communicating with a particle separator, wherein at least two a are arranged in the partition 25 (42, 44, 46), at least one of which is adjustable and connecting the heat transfer zones to conduct flue gases from the first zone to the second zone, or that - a partition wall 30 (94) is arranged in the flue gas outlet of the reactor chamber. , 96) leading to different particle separators (90, 92), and adjustable means (100) are arranged in the gas outlet (82) of the particle separators for adjusting the gas flows 35 flowing through the gas outlets. Reactor according to Claim 7, characterized in that the partition wall (34) is arranged vertically in such a way that it divides the flue gas draft of the upper part of the reactor into a first upstream and a second downstream zone. Reactor according to Claim 8, characterized in that openings (42, 44, 46) are arranged in the partition wall (34) at at least two different height levels. Reactor according to Claim 8, characterized in that at least two openings are arranged in the partition wall (34) at the same height level. Reactor according to Claim 8, characterized in that the second heat transfer zone (36) is divided into vertically adjacent channels (74,76,78) by at least one vertical partition (70, 72) arranged substantially perpendicular to the partition wall (34). Reactor according to Claim 11, characterized in that adjacent, adjustable openings (42, 44, 46) which open into different channels (74, 76, 78) are arranged in the partition wall (34). Reactor according to Claim 7, characterized in that the partition wall (34) is at least partially cooled. Reactor according to Claim 7, characterized in that the walls of the heat transfer zones are formed by water pipe walls (30). 30 Reactor according to Claim 7, characterized in that heat transfer elements (54, 56) are arranged in the heat transfer zones. Reactor according to Claim 7, characterized in that the openings (42, 44, 46) in the partition wall are steplessly adjustable. 16 b 5 41 7 Reactor according to Claim 8, characterized in that the openings (42, 44, 46) are provided with adjustable flaps (48, 50, 52). Reactor according to Claim 17, characterized in that the flaps at the same level are adjustable at the same time. Reactor according to Claim 7, characterized in that the particle separator is a horizontal cyclone (14). Reactor according to Claim 7, characterized in that the particle separator is a ceramic filter. Reactor according to Claim 7, characterized in that the particle separator is a vertical cyclone (80). Reactor according to Claim 7, characterized in that the partition wall is horizontal and divides the upper part of the reactor chamber 20 into two overlapping zones. Reactor according to Claim 22, characterized in that the upper zone is divided into adjacent channels by one or more vertical partitions arranged substantially perpendicular to the partition and in that the partition has at least one gas flow opening for each channel. Reactor according to Claim 7, characterized in that the partition wall is inclined and divides the upper part of the reactor chamber into two partially overlapping zones. i7 8 5 417