FI108251B - Method and device for increasing the capacity of a boiler plant - Google Patents

Description

108251

The present invention relates to a process for increasing the capacity of a boiler plant as well as to energy production and fuel treatment capacity according to the preamble of claim 1. The invention is suitable, among other things, for increasing the proportion of electric power, especially in plants using fluidized bed boilers and for increasing the capacity of recovery boilers.

The invention also relates to an arrangement for carrying out the method.

15 In steam boiler plants, electric power is generated in a steam turbine with steam heated by the thermal power of the fuel. However, much of the thermal energy cannot be used to rotate the steam turbine, but the low-temperature steam from the turbine 20 is condensed or the heat contained in it is fed to the district heating network. If the heat demand is high enough, the overall efficiency of the plant is good, since all the energy produced can be utilized. Usually, however, the need for electricity is greater than 25 thermal energy and, since heat cannot be conducted very far from the plant, thermal energy is wasted. Therefore, it would be advantageous to increase the share of electricity production so that the quality of energy produced by the plants better meets the need. In addition, it would be advantageous to be able to adjust the ratio of electrical energy produced to thermal energy according to the energy requirement.

1 'One arrangement for combustion is a fluidized bed boiler. In a fluidized bed boiler, solid fuel is typically burned in a boiler furnace in a stepwise fashion. In the fluidized bed at bottom 35 of the furnace, where the fuel and the inert bed material float mixed with the air jets from the bottom of the boiler, there are underfree conditions, so that the fuel does not burn in the fluidized bed and the volatile components are gasified. In the part above the fluidized bed, called the freeboard, the gassed fuel is burned to completion by means of secondary and tertiary air supplied above the fluidized bed 5. The temperature of the Lei layer is typically 700 to 900 degrees and the fuel is fed there by dropping or by means of a jack screw. The fluidized bed is maintained in the fluidized bed by the amount of primary air supplied below the bed, which is typically about 40% of the total amount of air fed to the boiler. The remaining 60% of the air is fed to the freeboard above the fluidized bed, typically about 4-8 meters above the surface of the fluidized bed. In the fluidized bed, fuel is gasified, whereupon the volatile matter rises to the freeboard where it is burned by a stepwise supply of air.

Combustion in fluidized bed boilers can be divided into four zones as follows:

A fluidized bed in which the fuel gasifies and 20 residual coke · burns at a temperature of approximately 750 to 900 degrees Celsius. The fluidized bed is held in a fluidized space by blowing through it with sufficient air through a grate.

Above the fluidized bed, a splash zone of about 3 to 5 ft-25 ft, which is generally not fed with additional air. In this region, there is no significant change in the composition of the gas, however, the remaining free oxygen in the primary air reacts with the fuel to generate heat.

. 30 - Secondary air is injected above the splash • area, causing the gases to burn and the temperature to rise.

Typically, the temperature in this range is from 800 to 1400 degrees.

- At the top, before the first 35 heat exchangers entering the flue gas stream, there is a burn-out. a zone in which the combustion air factor is increased to more than 3,108,251 by one and the excess air is allowed to burn off gas and particles.

The amount of fluidized air in the furnaces of the boilers corresponds very well to the amounts of air used in typical fluidized bed gasifiers, and thus the composition of the gas above the fluidized bed surface and below the secondary air corresponds to the gas produced in special gasifiers. This can be seen in the sharp rise in temperature after the secondary air supply.

In circulating fluidized bed boilers, the fluid medium circulates through the top of the boiler to the cyclone on the side of the furnace, where the flue gases and fluidized media are separated. The fluid fluid is returned to the bottom of the boiler and the fuel used is fed to the recovery unit. The gases are introduced into the convection part after the solid particles have been separated. The particle stream returned to the furnace mixes only the amount of gas required by the gas trap. Thus, the mixture of fuel, fluid medium and circulating gas is extremely under-expressed, so that before the fuel enters the furnace, it gasifies strongly. In circulating fluidized bed boilers, as in fluidized bed boilers, the combustion air is led to the fire-chamber by blowing upwards from its lower part and through the connections located in the lower part of the furnace. The phasing of the combustion air is almost exclusively due to poor horizontal mixing of the furnace. In a circulating fluidized bed boiler, the fuel mixes with air mainly in the vertical direction. Due to the slow mixing in the horizontal and horizontal direction, • there are strongly under-exposed areas near the fuel feed points where gasification of the fuel and combustion of the fuel occurs as it moves upstream of the furnace.

35. ,. Due to the phasing, it is possible to remove gas from the gasification area of the combustion chamber and to operate it at the inlet temperature of the gas turbine by burning the removed gas in the combustion chamber of the gas turbine. Since the highest fluidized bed boiler has a maximum temperature of 900 ° C, the efficiency of the gas turbine would otherwise be poor due to the low temperature of the flue gases, and combustion of the evacuated gas increases the efficiency significantly by increasing the inlet temperature. This method is called "top-ping" and is mainly used in combined-cycle power plants. In this method, the furnace must be pressurized so that the combustion gases and the exhaust gas can be used in a gas turbine. Topping does not increase the total power of the boiler, nor can additional fuel equal to the amount of gas removed be fed into the boiler. Top processes are described, for example, in EP 340 351 and WO 94/02711.

In oil burners and coal dust burners, the phasing is carried out in different stages of the burner flame by means of air flows to the flame. In wall burners, which are mainly used today, fuel is usually fed from the center of a rotation symmetric burner and usually two air supply channels around the fuel passage or nozzle. Near the fuel feed point, the flame is very sub-free and reducing and there is strong gasification in this area. The fuel is burned to the end of 25 by secondary and tertiary signals fed in stages to the flame. In addition, additional air can be supplied to the top of the furnace if required.

In a boiler for soda, black liquor is injected by spraying it. . 30 boilers at a suitable height. The black liquor droplet dries and partially burns when dropped, forming a glowing clump at the bottom of the boiler. The air from the recovery boiler is also phased in at different heights and the combustion is complete only after all the air registers. Thus, the lower-35 portion of the recovery boiler operates on the same phased principle as the fluidized bed boiler.

It is an object of the present invention to provide a method by which the power of a phased boiler can be increased and in particular the proportion of electric power 5 produced by it.

The invention is based on the fact that in stepwise combustion, gas is sucked from the under-exposed area of the furnace, which is burned separately in a separate gas turbine or in a separate boiler. The furnace or burner can then be supplied with an amount of additional fuel approximately equal to the heat of the suction gas to compensate for the heat removed.

More specifically, the method 15 of the invention is characterized by what is set forth in the characterizing part of claim 1.

The device according to the invention, in turn, is characterized by what is stated in the characterizing part of claim 13.

The invention provides considerable advantages.

** 25

The invention can advantageously increase the production capacity and power generation efficiency of an existing power plant when the combustible gas formed in the early stages of fuel combustion is vacuumed off outside the furnace 30 for efficient use. Combustion • always produces a flammable gas first, which burns completely if there is sufficient oxygen and temperature. The maximum amount of gas to be vacuumed depends on the fuel but corresponds to the amount of gas formed by the volatile components of the fuel. Changes to the old process are minor and mainly concern 108251 6 automation. Benefits can also be obtained in the form of cheaper district heating if the plant has a gas or oil boiler space where product gas can be burned. The method is well suited for leveling the consumption peaks of small power plants, because it provides advantageous additional energy from the same boiler when needed and does not require the use of expensive gaseous or liquid. The invention can be applied to a variety of plants as long as the incineration is carried out either in a boiler or in a burner with sufficient phases.

10 The operation of the system, and in particular of the gasification portion, is balanced by the fact that the gasification process serves as a side-line of a large and stable process and is therefore less sensitive to interference than small gasifiers where the gasification process 15 must also produce the heat required for gasification. In the process of the invention, the heat required for gasification is obtained by the combustion process, since heat is radiated from the exhaust zone down to the fluidized bed and maintains gasification of the fuel.

Vacuuming the gas from the boiler does not reduce the efficiency of the boiler, but more fuel can be fed into the same boiler, ie more fuel can be gasified, but only the amount of gas burned at the top of the furnace as before. The additional power obtained by gasification is limited by the decrease in the temperature of the bed and the fact that the fluidization rate or the amount of the lowest air (primary air) in the recovery boiler cannot be increased beyond 30 within certain limits so as not to disrupt the boiler. si. However, a large boiler can provide considerable fuel surcharge to replace the expensive fuel in a gas turbine or gas boiler. The increase in fuel efficiency can be up to 20-30%.

35

It is advantageous to purify and cool the pressurized gas from an unpressurized boiler for compression, so that the cost of the necessary accessories remains reasonable. In pulp mills, the gas produced by the recovery boiler can be used as fuel for a lime kiln, a supercharger 5 gas turbine or an auxiliary boiler.

The invention will now be explained in more detail with reference to the accompanying drawings.

Figure 1 illustrates one embodiment of the invention.

Figure 2 illustrates another embodiment of the invention.

Figure 3 illustrates a third embodiment of the invention.

15

Figure 4 shows a fourth embodiment of the invention.

Figure 5 illustrates a fifth embodiment of the invention.

Figure 6 shows a sixth embodiment of the invention.

The invention is based on the suction of gas in phased combustion from an area where the flame is strongly sub-free and produces gas which is further burned by supplying air to it. In a fluidized bed boiler the gas is drawn from the furnace 24 of the boiler 1 from the area where the gas quality is best. Vacuumed gas is cleaned and pressurized to high pressure so that it can be used, for example, as a gas turbine fuel. This generates quite a single to thirty gas pressure carburettor, and can efficiently increase power generation efficiency or fuel efficiency in older plants as well.

The invention can be applied, for example, in connection with layered floating-35 spaces. The fluidized bed boiler 1 has air nozzles 2 at the lower part of the furnace 24, from which up to 108251 s of air are blown up into the fluidized bed 1 above the nozzles. The fluid medium is usually sand. The fuel is fed through the connections 4 and forms a bed floating with the fluid medium where the fuel and air 5 are effectively mixed. The velocity of the fluidizing air should be low enough to keep the fluidized bed low enough. At the same time, the floating air is the primary air of the boiler 1, which accounts for about 40% of the total amount of air in the boiler, so that the amount of air is not sufficient to burn up the fuel. However, due to efficient mixing, the fuel reacts well with the amount of air available and gasifies well. The heat emitted from the top of the boiler improves the boiler efficiency.

Above the fluidized bed 3 there is a splash zone 9 in which jets of fluid particles and gas particles of the gasification towers rise. No air is added to this area, so only the fuel reacts with the rest of the free oxygen. The actual combustion of the gaseous fuel takes place in the upper 20 boiler. Above the splash zone 9, additional air is supplied to the boiler via the secondary air ducts 5, whereupon the gaseous fuel is ignited and the temperature in this layer rises to between 800 and 1400 ° C. Secondary air is fed so much that the total air factor rises to about 25, so that the fuel in this floor is almost exhausted. The rest of the air is fed through the tertiary air connections 6 to the burn-out zone 11, which aims to burn any remaining gases and particles.

From the burnout zone 24, the flue gases rise to the top of the boiler - 1, which has first heat exchangers, which are generally steam circuit superheaters 7. From the superheaters 7, the flue gases are led to the heat exchangers 8 in the convection duct and further to cleaning and chimney.

35 9 108251

The gas used as fuel for the gas turbine or the separate boiler is vacuumed from the boiler 1 through the connections 12 located above the fluidized bed. The connections can be arranged in many ways, but the gas must be vacuumed evenly to prevent the furnace 24 currents from being unduly disturbed. Preferably, the inlet connections are evenly spaced around the walls of the boiler while being as open as the air supply connections. In order to obtain the desired gas from the furnace 24 and not to vacuum the exhaust gas from the upper furnace 10 which can no longer be burned, the gas extraction ports 12 must be located below the secondary air connections 5. The evacuated gas contains impurities and fluid fluid which cannot be discharged e.g. into a gas turbine. The gas purification is carried out in a manner known per se, the first purification step at least in the fluidized bed boiler being preferably cyclone 14, or other apparatus for separating coarse particles. The particulate contaminants separated from the cyclone 13 and the fluidizing medium are fed back through the fluidized bed 3 via a single 14.

20

For turbine operation, the cleaning result is completed by a scrubber 16, where the gas is led by line 15 or by heat-resistant filters. The advantage of the scrubber 16 is that it can cool the gas there. After scrubber 16, the gas 25 is led in line 17 to a compressor for compressing the gas to operating pressure and the product gas in line 20 to be incinerated or otherwise utilized. If the gas is burned in an auxiliary combustion boiler, purification by simple cyclone separation may be sufficient and compression may not be necessary. The compressor 18 is rotated by a separate motor 19 -v or the compressor may be a gas turbine compressor if the product gas is directly fed to the turbine intake air.

In the solution shown in Figure 2, cyclone 21 is placed inside a fluidized bed 3 within furnace 35 and gas is aspirated into cyclone ... 21 through pipe 22 and fluidized material and solid particles.

the cartridges exit back to the bed via tube 23. Otherwise, the apparatus is as described above.

Figure 3 illustrates a circulating bed fluidized bed boiler 25. In a circulating-5 ladder, the combustion air is blown from the bottom of the boiler 25 by the upstream bottom ports 27 and the secondary air ports 26 in the lower part of the furnace 24. 10 with the flue gases into the cyclone 32. In the cyclone 32, the fluid is separated from the flue gases which are introduced into the convection section 35 which, as usual, has heat exchangers 8.

The fluid medium drops into the lower part of cyclone 32, from where it is fed back to the lower part of the furnace 24 in the region 15 of the air connections 26. Fuel is supplied to the boiler via a separate fuel inlet 29 directly into the air inlet 26 or into the fluid medium return conduit 34.

Because the gases coming from the cyclone fluidized fluid are 20 exhausted flue gases and the amount of air needed for aeration of the gasification so small that the small fuel particles that are entrained in the fluidized medium consume much of the oxygen that enters, 24 very little oxygen. Thus, the mixture of fuel, fluidized media and circulating gas is extremely under-expressed, so that before the fuel enters the furnace 24, it is strongly gasified by the heat of the fluidized medium and the hot flue gases. Direct fire; The fuel supplied to the housing 30 is phased in approximately · -. gentle fuel feed point. In a circulating fluidized bed boiler, the fuel mixes with air mainly in the elevation and horizontal mixing, so there are strongly under-35 locations near the fuel feed points where gasification and phasing occur. . the fuel burns out as it moves up * 108251 11 in the furnace. Thus, from the proximity of the fuel feed lines 29, gassed fuel can be sucked in a manner similar to fluidized bed return conduit 34.

5

In a boiler using coal dust or oil as fuel, the stepping occurs in the burner and not in the boiler area; wall combustion technology in which the burners 36 are located on the boiler wall and their flames are directed toward the center of the boiler. The combustion air is supplied mainly through the burners in phases. In the typical carbon burner shown in Figure 4, fuel is supplied from the center of the burner and surrounded by a two-piece air duct 38, 39.

15 The structure of the oil burners is similar to that of Figure 4. The air supplied with the carbon dust is effectively mixed with the fuel and gasifies under reducing conditions in the gasification zone 41 near the flame base, providing additional air to the gasified gas, thereby igniting and partially 38 and the fuel burns out in area 43

From the flame reducing region 41, gas from the fuel can be absorbed in a manner similar to that of fluidized bed boilers. The suction tube 40 is positioned near the burner tip so that it extends to the gasification zone 41. Because in modern phase burners, the air and fuel flow 30 backgrounds accurately designed, suction tube 40 layout and. . size must be accurately determined for each burner model so that burner operation is not disrupted. The suction pipes can be placed in each burner or in some of them.

Figure 5 shows a recovery boiler. The upper part of the boiler with the heat exchangers is similar in structure to the upper part of the fluidized bed boiler or coal dust boiler with superheater 7 and convection parts 35. The black liquor used as fuel for the boiler is injected into the furnace 24 through fittings 45. The fuel droplets dry-5 and burn when dropped, and the non-combustible material collects on the bottom of the boiler to form a soot 48. At the edges of the soot 48, green liquor is removed through the connections 49 and returned to the pulping process. The air is supplied to the furnace in three steps by the links 44, 46 and 47. At the first air connections 10 47, the mixture of black liquor and air is very under-aired, so that only black gas is gasified in this area. Thus, flammable gas can be drawn from the firebox below or approximately below the lower air lines 47. The gas is aspirated by conduit 50 and purified for use with purifier 51. The invention can be used to increase the caustic treatment capacity of an expensive boiler investment. Because the recovery boilers are very expensive, they are sized to a minimum and there is a clear need for additional capacity.

20

The heat value of the gas obtained by the process described above is relatively low because it contains a large amount of inert components such as nitrogen and water. The calorific value of the gas can be increased by reducing the amount of nitrogen and / or water in the gas. In the process of Figure 6, the gas is enriched by reducing its nitrogen content. This is accomplished by dividing the fire furnace partially by wall 52 into two portions by supplying additional fuel to one of the spaces. The space into which the extra spill is fed is smaller than the rest of the furnace, so. 30 this space gets less air from the bed. Since the ratio of air volume to fuel volume is lower in the region where additional fuel is supplied, the calorific value of the gas in this state is higher than that of the gas in the adjacent state. The amount of air entering the compartments separate from the bed can be determined based on the surface areas (x, y) of the 35 beds.

108251 13

Excess gas that has been gassed is removed from the furnace as high as possible because the flames in the overhead main combustion area radiate energy downward as some bed material piles run high in the fire-5 chamber. Energy in the main fuel zone increases the energy at the top of the smaller gasification area and facilitates the decomposition of fuel tars.

In addition to the above, the present invention has other embodiments.

In addition to the gas turbine, the sucked product gas can be burned in an auxiliary boiler, lime kiln or other boiler where additional energy from gas combustion is required. One of the ways of gasification could be the carbon hardening of the engineering and steel industries. The process involves exposing steel to high-temperature reducing carbon monoxide-containing gas, thereby diffusing carbon into the steel surface, which significantly increases the hardness of the steel by combining the steel with rapid cooling. In this case, the coal furnace would be in line immediately after the cyclone, which could be followed by normal combustion or purification and high pressure before it. The method could be used to calculate the fuel cost of engineering workshops.

The method according to the invention is particularly suitable for old boilers, but it can also be advantageously used in new boilers, whereby a boiler of a certain size. 30 provides higher than normal power. Use of gas and fixed. Of course, the combustion proportions of the substance in new boilers can be more freely chosen than in existing boilers, since the equipment can initially be designed to operate in a certain way. The method can be applied 35 for auxiliary or starter burners and for wet fuels if the fuel is dried prior to combustion 108251 14 to improve gas quality.

•

Claims (23)

A method of increasing the capacity of a boiler plant, wherein air and fuel are fed into a fireplace (24), the air being fed at a first stage of the fuel in a lesser amount than is needed for complete combustion of the input fuel, the fuel is gasified, air is fed into the fuel at at least one subsequent stage of ignition and combustion of the gasified fuel, and the pressure in the fireplace (24) is substantially at the same level as the ambient pressure, characterized by the removal of gas formed by the fuel from the fuel. the mixture of fuel and air by suction from a reducing area with air deficiency before admixture of additional air into the mixture, and the gas removed from the fireplace (24) is used in: - a separate device which is separated from the boiler process. 30 2. A method according to claim 1, characterized in that an additional fuel quantity in the nearest corresponding heat value for the gas quantity removed by suction is fed into the fireplace (24) or in the burner, to compensate for the heat quantity removed. 5 3. Process according to claim 1, characterized in that the gas removed by suction is cleaned and used as fuel for a gas turbine. 10 Method according to claim 1, characterized in that the gas removed by suction is burned in a separate boiler. 5. A method according to claim 1, characterized in that the gas removed by suction is burned in a blast furnace. Method according to any of the preceding claims, wherein the boiler is a fluidized bed boiler and air and fuel are fed into the lower part of the fireplace (24), the air at a first stage being fed into the fireplace (24) into a smaller amount than is necessary for complete combustion of the input:. . the amount of fuel, whereby the fuel is gasified, and 30. air is fed into the fireplace (24) at at least one subsequent step above the fuel feed point and the first air feed point, characterized in that - the gas formed by the fuel is sucked from the fireplace (24) below a second air entry point and in the fluid bed of the fluidized bed. The method of claim 1, wherein the boiler is a soda boiler, characterized in that gas is drawn from an area between the second air inlet point 10 (46) and the green liquor outlet point (49). The method of claim 1, wherein the boiler is a boiler with circulating fluidized bed, characterized in that gas is drawn from the fireplace (24) from a reducing area in the vicinity of the feed point (29). The method of claim 1, wherein the boiler is a boiler with circulating fluidized bed, wherein the circulating bed material is fed into the fireplace (24) through a return line (34), characterized in that fuel is fed into the return line (34) and gas is sucked off. an area between the fuel feed point (30) and the fireplace (24). 25 The method of claim 1, wherein the boiler is a coal-fired boiler or an oil-boiler, wherein one. Stage burner is used, characterized in that gas is drawn from the reducing area of the burner position. 11. A method according to claim 1, wherein at least one take-off or additional burner is used in the boiler, characterized in that gas is drawn from the reducing area for the law of the start-up or supplementary burner. Process according to any of the preceding claims, characterized in that moist fuel, which is dried before combustion, is used in the boiler to improve the quality of the gas intended for suction. Device for increasing the capacity of a boiler plant, comprising: a boiler (1) having a fireplace (24), 15. appliances (4) for feeding fuel into the fireplace and for combustion thereof, - appliances (2) for mixing air in the fuel intended to be fed into the fireplace (24) at a first stage 20 for gasification of the fuel, and - at least one set of second means (5, 6) for feeding air into the air-fuel mixture at at least one subsequent stage for ignition and combustion of the fuel, characterized by - at least one bounce for suction of the gas from the reducing area after the fuel entry point before the air enters the fuel at the second stage, and 108251. - at least one device in which suction fuel can be used and which is separated from the boiler process. 5 Device according to claim 13, comprising: - a fluidized bed boiler (1), having a fireplace (24), 10 means (4) for feeding fuel into the fireplace, - means (2) for supplying air at a first step in the fireplace (24), and at least one set of means (5, 6), arranged above the first air inlets (2), for supplying air into the fireplace (24) at at least one subsequent step, characterized by at least one stud provided below the other air inlets (5) for suction of gas from the fireplace (24). Device according to claim 14, characterized in that in the gas suction pads (12) are arranged in the fluidized bed (3). 30 v 108251 26 Device according to claim 15, characterized by a cyclone (21) arranged in the fireplace (24), which is connected to the suction pads (22) for the gas. Device according to claim 13, characterized by a cyclone (13) arranged outside the fireplace (24) and a washer (16) for purifying the gas sucked from the fireplace (24). The device of claim 13, wherein the boiler is a soda boiler, characterized by at least one bounce (50) for suction of gas from an area between the second air inlet point (46) and the green liquor outlet point (49). 15 The device of claim 13, wherein the boiler is a boiler with circulating fluidized bed, characterized by at least one bounce for suction of gas from the fireplace (24) from a reducing area in the vicinity of the feed point (29) of the fuel. Apparatus according to claim 13, wherein the boiler comprises a boiler having a circulating fluidized bed, comprising a return line (34) for feeding into the fireplace (24) of the circulating bed material, characterized by means (30) for supplying fuel in the furnace. return line (34) and for suction of gas from one. area between the fuel feed point (30) and the fireplace (24). 30 Apparatus according to claim 13, wherein the boiler is a coal powder boiler or an oil boiler, using a phase-divided burner (36), characterized by means for sucking gas from the reducing area of the burner (36) position. Apparatus according to claim 13, wherein the boiler comprises at least one starting or supplementary burner, characterized by means for suction of gas from the reducing area for the location of the supplementary or starting burner. Device according to any one of claims 13 to 22, characterized by a wall (52) which divides the fireplace partially into two compartments with different volumes, and means for supplying additional fuel into one of the compartments. <4 '(