Abstract:
A cooling system for air ports and other ports in furnace walls includes a cooling medium pumping system and ports provided with a cooling medium piping or channels inside the metallic port material. The liquid flow generated by the cooling medium system cools the ports. The ports are constructed of a casting material, and the ports are provided with a cooling liquid flow, which passes in a piping or pipings or channels inside the casting material of the ports.

Description:
[0001]    The present invention relates to a cooling system for ports in a wall of a boiler. A typical port is an air port for feeding air to a boiler furnace. In addition to air ports, there are a number of openings, apertures, holes or passages in boiler walls for feeding substances, such as fuel or gas or chemicals, or for different instruments, devices, or equipment, such as control devices. These structures are called ports in connection with this invention. In particular, the invention relates to air ports and other ports of a black liquor recovery boiler. 
         [0002]    Black liquor produced in pulp manufacture is combusted in a recovery boiler, which is an essential apparatus in the chemical recovery circulation of a sulfate and other Na-based pulp manufacturing processes. The cooking chemicals from a digester are turned into a form suitable for the recovery process. In a sulfate process the most important chemicals are sodium and sulfur. Organic substances dissolved in black liquor during digestion are combusted in the boiler producing heat which is used, on one hand, in converting the inorganic compounds contained in the waste liquor back into chemicals to be used in the digestion and, on the other hand, in the production of steam. The inorganic matter of the waste liquor melts in the high temperature of the boiler and runs down as smelt to the bottom of the furnace. 
         [0003]    The smelt is taken from the bottom of the boiler along cooled smelt spouts to a tank in which it is dissolved into water or weak white liquor to produce soda lye, i.e. green liquor. The main components of the smelt and thus also of the green liquor in a sulfate process are sodium sulfide and sodium carbonate. The green liquor is then transported to a causticizing plant for white liquor production. 
         [0004]    The air required for the combustion of the organic material in the black liquor is led to the furnace of the recovery boiler from air distribution channels arranged at various levels around the furnace, through the air ports in the walls of the furnace. A port opening is created by bending waterwall tubes outwardly and away from each other. The air is most commonly introduced into the furnace at three levels. Lowest, there is a primary air level, above that a secondary air level, and highest, above the liquor nozzles, a tertiary air level. There may as well be more than three air levels in the boiler. 
         [0005]    Typically nozzles are disposed in the air port openings in the boiler wall so as to direct air into the furnace. Nozzles have typically been manufactured of different metal plate materials by welding. The nozzles are attached onto the tube panel walls of the furnace e.g. by welding or in some other mechanical way. Air ports may also be constructed of a cast material seal-welded to the wall tubes forming the opening, 
         [0006]    Combustion air is led in the air ports from air ducts surrounding the boiler. The air ports and the structures in the vicinity thereof are cooled by the flowing combustion air, and by conduction to the furnace walls. Combustion air temperature is typically 20-200° C., depending on which combustion air is considered. Normally the lowest air flow, which is called primary air, has the highest temperature, and the air flows, which locate highest in the furnace have the lowest temperature. The air feeds (e.g. tertiary) above the black liquor feed level or levels (above the liquor guns) are often without preheating. When the cooling takes place via the air flow through the air port, the cooling effect is clearly less effective than it would be with water, either with boiling or with unboiling water. This is due to the thermodynamic and heat transfer properties of the two media (air vs. water). Also cooling via conduction from the air port to the furnace wall tubes, which are cooled by boiling boiler water, is much less effective than it would, if water would be in direct contact with the port. This is because the distance from the cooled inner surface of a water tube to the tip of the uncooled front face of the air port is long, and the heat transfer efficiency between the cast air port and the cooling furnace wall tube is not very effective. To make the cooling effect via the furnace wall tubes more effective, sleeve-type airports have been used. In this construction the airport has been made of plate material, which is bended into the right shape and welded into the furnace wall tubes. The potential drawback of this design is related to such boiler design and operation, which causes splashing of smelt or black liquor into the port The main components of the smelt in a sulfate pulping process are sodium carbonate and sodium sulphide. The smelt splashes on the outer side of the air port cause rapid heating of the structure of the air port up to the melting point of the smelt, whereby the salts cause corrosion and erosion in the air ports. Rapid changes in the temperature generate thermal weariness and stress corrosion cracking in the structures of the air port and even in the encircling tubes of the furnace. Especially harmful are the varying temperature differences between the wall tubes and the air port sleeve material, especially their fastening welds. 
         [0007]    The problems, which are described above for air ports, are valid also for other ports and for finned areas of the furnace, where the width of the uncooled area is too wide. These uncooled areas are related to various ports, openings, apertures or lance-type connections in the walls of a boiler furnace. In addition to air ports, there are a number of openings, apertures, holes in furnace walls for feeding substances, such as fuel or gas, or for different devices, such as control devices. These structures are called ports in connection with this invention, and effective cooling is typically needed in these ports. The critical width for the uncooled area in the lower furnace of a recovery boiler is typically 15-25 mm. Also in these cases the design can be improved by introducing specific cooling. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    The present invention is intended to ensure that the temperature of air ports or other ports and the structures of the wall of the furnace in the vicinity will not rise too high in view of corrosion, temperature changes, cracking and tightness. This results in remarkable decreases in repair and shutdown expenses. Especially the primary air ports closest to the smelt bed are exposed to detrimental effects of the smelt. In addition, the invention is to provide an apparatus easy to maintain and repair. In this way, it is possible to decrease repair and shutdown costs significantly. Further, the arrangement according to the invention decreases thermal stresses directed on the tube walls of the furnace. 
         [0009]    The present invention, which eliminates (or at least reduces) the cooling problem of the air port and other ports of boilers, introduces effective cooling into the ports. The present invention allows the use of more efficient cooling media than air. 
         [0010]    The cooling system for air ports and other ports in furnace walls according to the present invention comprises a cooling medium (liquid) pumping system and ports provided with (preferably in connection with the casting process) cooling medium piping or channels inside the metallic material. The liquid flow generated by the cooling medium system cools the ports so that the temperature of the air ports and other ports is maintained low enough for extending the useful life of the ports and structures in the vicinity thereof The ports are constructed of a casting material and provided with a cooling liquid flow, which passes in a piping or pipings or channels inside the casting material of the ports. The cooling medium is a liquid, preferably water. The working pressure of the water can vary from a pressure lower than atmospheric pressure to a pressure slightly higher than atmospheric pressure. 
         [0011]    The whole cooling system comprises liquid tanks, cooling liquid pumps, heat exchangers, control devices, electors. which are typically used in cooling medium circulation systems. Combustion boilers can have a cooling medium circulation system, to which the cooling system for air ports or other ports according to the invention can preferably be connected. Recovery boilers have smelt spouts for discharging smelt from the bottom of the furnace. The spouts are typically constructed of a double wall trough, with a continuous flow of cooling water passing between the inner and outer walls. The cooling medium flow used for cooling air pods or other ports can be wholly or partly connected to the smelt spout cooling system. Heat recovered in the cooling water can be used for warm water production, heating the boiler plant or for any other suitable purposes. 
         [0012]    According to an aspect of the invention the cooling liquid piping is in metallic connection with the casting material, whereby an efficient heat transfer from the port to the cooling liquid is obtained. The cooling liquid flow is leak-safe in the port zone, because the cooling liquid piping is inside the casting material. The material of the ports and the material of the cooling liquid piping may be chosen appropriately based on the operating conditions The flow amount and temperature of the cooling liquid may be chosen based on the corrosiveness of the conditions, the material and the construction of the port. The cast is preferably made of metal. A combination of metal and ceramic may be made to make the cast more heat- and corrosion-resistant. 
         [0013]    The port construction consists of a casting port and a collar part, which is weldable to the wall tubes. The collar may be made by casting or some other method, e.g. made of round bar. The weldable collar part may in some applications be omitted, whereby a longer lip of the cast port compensates its role. 
         [0014]    The piping or channels in the cast port can be arranged so that the cooling medium is introduced into the cast through one inlet tube. The inlet tube has a junction, or junctions where it is divided into two or more tubes, which continue separately around the opening of the port. The tubes can be connected together just after the travel around the opening, so that the heated medium is led away through one outlet tube. 
         [0015]    The cast port can also have two or more inlet tubes for the cooling medium, which tubes continue separately through the cast port so that the cooling medium is led through several outlet tubes from the cast port. The tubes, which go through the cast port, are totally inside the casting material, but some parts thereof may be outside the casting material. Heat transfer between the cooling medium and port is, of course, the more efficient the more the tubes are inside the port. 
         [0016]    The flow of the cooling medium through the cast can be arranged by means of channels made into the cast during the casting stage. The channel or channels go around the opening of the port. The cooling medium can be fed into the channels through one or more inlet tubes, and the cooling medium is led from the cast through one or more outlet tubes. The cast is provided with one or more inlet tubes for introducing the cooling medium into the cast and with one or more outlet tubes. 
         [0017]    The cooling arrangement may be used for primary, secondary, tertiary, and for upper air ports in recovery boilers. In these cases air is introduced into the furnace via the opening of the port. The cooling arrangement may be used for liquor gun ports in recovery boilers. In these cases the liquor gun is located in the opening of the port, or liquor is sprayed through the opening of the port into the furnace. 
         [0018]    The cooling arrangement may be used for start-up, load and malodorous gas (non-condensable gas) burners in recovery boilers. In these cases the burner is located in the opening of the port. The port can be a part of the burner. Moreover, the cooling arrangement may be used for smelt bed camera ports, for instrument ports and for inspection and observation ports in recovery boilers. The cooling arrangement may also be used for entrance doors in recovery boilers. 
         [0019]    The cooling arrangement may be used for sootblower openings in recovery boilers, and for smelt spout openings and for smelt openings in recovery boilers. The port is part of the smelt spout or the spout is part of the port. The cooling arrangement may also be used for NO x  reduction agent injection ports in recovery boilers. The cooling arrangement is applicable especially in recovery boilers used for burning black liquor generated in the production of cellulose, but it may naturally be applied in other corresponding combustion devices as well. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0020]    At least one embodiment of the invention is described in more detail with reference to the appended Figures, of which: 
           [0021]      FIG. 1  illustrates an air port in a cutaway at a middle height of the port. 
           [0022]      FIG. 2  illustrates an air port in a cutaway along a lateral direction of the port. 
           [0023]      FIG. 3  illustrates a general view of a cast port construction. 
           [0024]      FIG. 4  illustrates a cooling system having a single air level. 
           [0025]      FIG. 5  illustrates a cooling system having three air levels. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]      FIGS. 1 AND 2  illustrate an air port structure according to the invention. Combustion air flows into a furnace  5  of a boiler through an air port  4 . The air port opening is formed by bending adjacent water wall tubes  1  apart so that the port assumes an elongated shape. The air port  4  is defined by a nozzle-like structure  2  which is disposed in the furnace wall and produced by casting. 
         [0027]    Prior to casting, the cast is provided with a tube ring  3  or two separate tubes. In the casting stage, the appropriate fitting of the tube ring assembly  3  inside the casting material has to be ensured. A collar  6  is fitted by welding in the opening formed of wall tubes  1 . The collar  6  may be made by casting or some other method, e.g. made of round bar. The facing surfaces of the air nozzle  2  and collar  6  are compatible for ensuring a sufficient tightness. 
         [0028]    Insulating material  7  may be used between the air nozzle  2  and wall tubes  1 . The collar  6  is welded (at  8 ) at the sides onto the wall tubes  1  and both at the top and at the bottom onto a fin  9 . Sealing material  10  may be used at the top and at the bottom between the nozzle  2  and the fin  9 . The air nozzle  2  is attached mechanically in some known way so that the facing surfaces of the nozzle  2  and collar  6  are in tight contact. 
         [0029]    Cooling liquid  12  passes from a cooling liquid feed pipe  11  into the tube ring  3  as the flow is divided into branching ducts of the ring  3 . The return flow  14  of the cooling liquid comes from a return pipe  13 . 
         [0030]      FIG. 3  shows a whole cast port  2 . Cooling medium is introduced through a pipe  11 . Cooling pipes or tubes  3  go separately around the opening of the cast port The heated cooling medium is discharged through a pipe  13  It is also possible that the cooling medium tubes are not located inside the nozzle-like port, but there is another cast piece, which is provided with a cooling system and which is in a close contact with the nozzle part. Especially the lower part of the nozzle is cooled by the other cast part. 
         [0031]      FIG. 4  illustrates a cooling medium circulation for one air level in the system according to the invention (a one “air level” system). The cooling liquid equipment comprises a cooling liquid tank  15 , piping  16 , valves  17 , pumps  18 , valves  19 , a pipe  20 , a pipe  21 , a manifold  22 , a nozzle-specific feed pipe  23 , a valve  24  in the feed pipe, a nozzle construction with its tube ring  25 , a return pipe  26 , a valve  27  for the return pipe, a collector tube  28 , a tube  29 , an air discharge tube  30 , a valve  31  for the air discharge tube, a return line valve  31 , a return tube  33 , a heat exchanger  34 , which may be of liquid/air or liquid/liquid type, a return tube  35  from the heat exchanger. 
         [0032]    In case of a liquid/air heat exchanger, an air fan  36  cools the cooling liquid and heated air  37  may be led into the boiler room or into the atmosphere. 
         [0033]    A pressurized flow for the cooling liquid is generated by means of pumps  18 . The cooling liquid flows via piping into wall-specific manifolds  22 . From the manifold  22 , a cooling liquid feed tube  23  leads to each air nozzle  25 . The flow of the liquid may be adjusted for each nozzle by means of valve  24 , which may be either manually or automatically operated. The liquid flow cools the air nozzle and the return flow is directed via return tube  26  to the return line. The return flows of the cooling liquids for the nozzles are collected together with a wall-specific collector tube  28  and return tube  29 . Via a common return tube  33  the cooling liquid flow is led into a heat exchanger  34 , wherein heat energy is transferred to air or liquid, depending on the application. 
         [0034]    The cooling liquid circulation may be provided with necessary devices for measuring the pressure and temperature.  FIG. 4  shows the positioning of the measuring devices, mainly in view of manual control. If automatic regulation devices for flow amount control are used, the number of measuring devices is bigger. 
         [0035]      FIG. 5  illustrates a cooling medium circulation for three air levels in the system according to another embodiment of the invention (a three “air level” system). The three air-level system has three air levels  39 ,  40  and  41  liquid-cooling system in parallel connection, The air levels may be primary, secondary and tertiary air levels. The main principle of the liquid-cooling system is the same as that of the one “air level” system of  FIG. 4 . The functioning of the system as a whole is ensured by choice of flow amounts and components. 
         [0036]    Heat recovered in the cooling medium according to the invention can be used to generate warm water, hot water, steam, or to heat up other heat transfer media. Said warm water, hot water, steam or other heat transfer media can preferably be used:
       for condensate preheating, make-up water preheating, feedwater preheating, combustion air preheating, heating a boiler house,   in an evaporation plant for water evaporation from waste liquor, from biosludge, or from a mixture of both materials;   for drying of bark, wood waste and other biomasses;   for heating or for district heating;   in the cooking plant of a pulp mill;   in the bleach plant of a pulp mill;   for pretreatment of chips in a pulp mill;   for drying of pulp in a pulp mill.       
 
         [0045]    Numerous alterations and modifications of the port arrangement herein disclosed will suggest themselves to those skilled in the art. For example, the port can be fitted to the wall tubes in another way than disclosed in connection with the Figures, and the invention is not limited to a certain way to fit or mount the port structure to the wall tubes of the boiler. All such modifications, which do not depart from the spirit of the invention, are intended to be included within the scope of the claims. 
         [0046]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment. it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.