Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
  • F16L43/00—Bends; Siphons
  • F16L43/001—Bends; Siphons made of metal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
  • B65G53/00—Conveying materials in bulk through troughs, pipes or tubes by floating the materials or by flow of gas, liquid or foam
  • B65G53/34—Details
  • B65G53/52—Adaptations of pipes or tubes
  • B65G53/523—Wear protection

Definitions

• the present invention relates to a pipe element in a transport system where the pipe element is traversed by a gas flow containing particulate material.
• a gas flow containing particulate material When the pipe element is subjected to the wear caused by the particles in the gas, erosion arises which successively wears out the pipe element.
• the invention aims to solve this erosion problem when transporting, for example, ash in pipe systems in a power plant.
• bends with a large radius are used according to conventional technique.
• an extra space may be provided in pipe bends beyond a point of deflection, where a cushion of powder accumulates, which receives and brakes the particles in the gas flow, in a so-called transfer chamber.
• Such bends are called T-bends because of their appearance.
• Pipe systems which include T-bends are advantageously used for transporting ashes from cyclones to ash coolers in, for example, PFBC plants or other coal- fired power plants.
• PFBC are the initial letters of the English term Pressurized Fluidized Bed Combustion.
• the risk of erosion is always great when bulk flows are de ⁇ flected, but the erosion rate can be reduced by increasing the radius of curvature of the pipe bend.
• T-bends the ends of a transfer chamber to a certain extent constitute erosion pro- tection by the formation of a protecting ash cushion.
• the bends are made of some hard metal, for example, Ni-hard, or, alternatively, the bends are lined with some ceramic.
• T-bends of the above-mentioned kind are shown, for example, in European patent publication EP 0108505.
• T-bends in cast white iron are standard components in PFBC power plants.
• the transport speeds are very high, up to 30 m/s. From tests carried out, it has been empirically proved that the radius of curvature for a bend which is internally lined with a hard metal layer must be about 3-5 m to be able to manage an operating time of at least 20,000 h. For reasons of space, it is not possible in practice to design all bends in a piping with such a large radius as 3-5 m. For that reason, T-bends are normally used.
• T-bends One problem with T-bends is that, in certain cases, hard thick coatings are formed in the outlet part. When the cross-section area decreases, the speed increases and so does the erosion in the T-bend downstream of the constriction. This is an acute problem in cyclone ash discharge systems which sometimes also lead to shutdown of the PFBC plant.
• the particles which are scattered over the pipe cross section in the inlet part of the bend will travel straight on until they hit the inside of the outer pipe wall.
• a certain deflection of the movement of the particles takes place because of the change of direction of the gas flow during the flow, but a large number of particles hit the pipe wall at a certain angle.
• the erosion is greatest, that is, the rate of wear is considerably greater in the inlet part of a bend than in other bend parts. Downstream of the impact zone, the particles are sliding along the periphery of the pipe bend. Here the erosion rate is considerably lower.
• Figure 3 describes how the particle density in a cross section perpendicular to the flow direction is changed with the radius of curvature of pipe bends with constant radii of curvature.
• d designates the internal diameter of the pipes, r the radius of curvature of the bend, 34 the flow of particle-gas mixture and 35 the impact zone where the particle density is greatest.
• the band of the particle-gas mixture decreases in thickness with increasing radius of curvature over the tubes 31, 32, 33.
• tube 33 the radius of curvature of which is greatest, the band is thin and uniformly distributed over the inside of the outer pipe wall.
• the object of the invention is to provide a transport device comprising pipe sections which are characterized by a low risk of erosion and an increased operating time.
• a pipe bend is used which has a large radius in its inlet part and then a narrower radius up to the outlet, that is, the pipe is designed with a decreasing radius of curvature in the flow direction.
• the radius can decrease continuously from the inlet to the outlet.
• the radius of curvature is to be large in the inlet part of the bend such that the particles in the gas flow hit the bend at a flat angle, the erosion rate thus becoming low.
• the radius of cur ⁇ vature may be relatively small.
• Figure 1 schematically shows a PFBC power plant
• Figure 2 shows an embodiment of the invention
• Figure 3 is a sketch showing the particle density in the cross-section area in a flow of particulate mate ⁇ rial in pipes with different radii of curvature.
• FIG 1 designates a pressure vessel surrounding a com- bustor 2 and a gas cleaning plant 3 which is symbolized by a cyclone.
• gas cleaning plant 3 dust is separated from combustion gases leaving the combustor 2 before they are supplied to a gas turbine (not shown) via a conduit 4.
• the gas turbine drives a compressor which, via the conduit 5, feeds the space 6 between the combustor 2 , the cleaning plant 3 and the pressure vessel 1 with compressed combustion air.
• the com ⁇ bustion takes place in a bed 7 of particulate material in the combustor 2.
• the fuel is supplied to the combustor 2 in the lower part of the bed 7 via the conduit 8 and nozzles 11.
• the combustor 2 is supplied with compressed air from the space 6 for fluidization of the bed 7 and for combustion of supplied fuel via a duct 9 and a bed bottom 10 with its nozzles 11.
• the combustor 2 includes tubes 12 for cooling the bed 7 and gene- rating steam for a steam turbine.
• dust consisting of ashes and residues of bed material are separated, which are fed out via the conduit 13 and a pressure- reducing discharge device 14 designed as a cooler and disposed in the duct 9.
• the discharge device is composed of a number of pipes 15 and transfer chambers 16, connecting an upstream pipe 15 to a subsequent downstream pipe 15.
• the dust is forwarded in the conduit 17 to a collecting container 18 with a filter 19 for cleaning the transport gas before this gas is passed out into the environment.
• FIG. 1 An example where a pipe bend accor- ding to the invention occurs is the conduit 13 in Figure 1. Since, in a gas cleaning plant in a power plant, a large number of dust cleaners in the form of cyclones occur, the number of bends required for the discharge from each respec ⁇ tive such dust cleaner is large and the space for laying conduits with a large curvature is limited, the need of bends with a small erosion is obvious.
• 20 designates a pipe bend shown in cross section, 21 the outer wall of the pipe, and 22 the inner wall of the pipe.
• the arrow designated 23 shows the direction of the gas- particle flow when it flows through the pipe.
• the pipe bend 20 in the figure is divided into two regions, A and B, with different radii.
• the outer wall of region A has the radius Rl which is larger than the radius R2 of the B region.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Branch Pipes, Bends, And The Like (AREA)
• Air Transport Of Granular Materials (AREA)
• Cyclones (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20404148

Family Applications (1)

Country Status (2)

Cited By (3)

Citations (4)

• 1996
  • 1996-10-07 SE SE9603650A patent/SE508405C2/sv not_active IP Right Cessation
• 1997
  • 1997-09-16 WO PCT/SE1997/001560 patent/WO1998015483A1/en active Application Filing

Patent Citations (4)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events