Part Wastegas Engineering 9 Control of Primary Particles 9.1 Wall Collection Devices The first three types of control devices we consider--gravity settlers, cyclone separators, and electrostatic precipitators--all function by driving the particles to a solid wall, where they adhere to each other to form agglomerates that can be removed from the collection device and disposed f
Part II Wastegas Engineering 9 Control of Primary Particles 9.1 Wall Collection Devices The first three types of control devices we consider--gravity settlers, cyclone separators, and electrostatic precipitators--all function by driving the particles to a solid wall, where they adhere to each other to form agglomerates that can be removed from the collection device and disposed of
9.1.1 Gravity Settlers It is an old, unsophisticated device that must be cleaned manually at regular intervals But it is simple to construct, requires little maintenance and has some use in industries treating very dirty gases, e.g., some smelters and metallurgical processes
9.1.1 Gravity Settlers It is an old, unsophisticated device that must be cleaned manually at regular intervals. But it is simple to construct, requires little maintenance, and has some use in industries treating very dirty gases, e.g., some smelters and metallurgical processes
Gravity settlers have little practical industrial use because they are ineffective for small particles At even modest velocities and common radi the centrifugal forces acting on particles can be two orders of magnitude larger than the gravity forces. For this reason centrifugal particle separators are much more useful han gravity settlers
Gravity settlers have little practical industrial use because they are ineffective for small particles. At even modest velocities and common radii, the centrifugal forces acting on particles can be two orders of magnitude larger than the gravity forces. For this reason centrifugal particle separators are much more useful than gravity settlers
There are many other variants on the centrifugal collector idea, but none approaches the cyclone in breadth of application. These devices are simple and almost maintenance-free. Because any medium-sized welding shop can make one, the big suppliers of pollution control equipment, who have test data on the effects of small changes in the internal geometry have been unwilling to make these data public When it is used to separate solids from liquids it is generally called a hydroclone
There are many other variants on the centrifugal collector idea, but none approaches the cyclone in breadth of application. These devices are simple and almost maintenance-free. Because any medium-sized welding shop can make one, the big suppliers of pollution control equipment, who have test data on the effects of small changes in the internal geometry, have been unwilling to make these data public. When it is used to separate solids from liquids it is generally called a hydroclone
If gravity settlers and centrifugal separators are devices that drive particles against a solid wail. and if neither can function effectively (at an industrial scale) for particles below about 5 um in diameter then for wall collection devices to work on smaller particles, they must exert forces that are more powerful than gravity or centrifugal force. The electrostatic precipitator (ESP)is like a gravity settler or centrifugal separator, but electrostatic force drives the particles to the wall
If gravity settlers and centrifugal separators are devices that drive particles against a solid wail, and if neither can function effectively (at an industrial scale) for particles below about 5 μm in diameter, then for wall collection devices to work on smaller particles, they must exert forces that are more powerful than gravity or centrifugal force. The electrostatic precipitator (ESP) is like a gravity settler or centrifugal separator, but electrostatic force drives the particles to the wall
The basic idea of all ESPs is to give the particles an electrostatic charge and then put them in an electrostatic field that drives them to a collecting wall. This is an inherently two-step process. In one type of esP, called a two-Stage precipitator charging and collecting are carried out in separate parts of the ESR. This type, widely used in building air conditioners, is sometimes called an electronic air filter. However. for most industrial applications the two separate steps are carried out simultaneously in the same part of the eSP
The basic idea of all ESPs is to give the particles an electrostatic charge and then put them in an electrostatic field that drives them to a collecting wall. This is an inherently two-step process. In one type of ESP, called a two-stage precipitator, charging and collecting are carried out in separate parts of the ESR. This type, widely used in building air conditioners, is sometimes called an electronic air filter. However, for most industrial applications the two separate steps are carried out simultaneously in the same part of the ESP
Figure 9.2 shows in simplified form a wire-and- plate ESP with two plates. The gas passes between the plates, which are electrically grounded (i.e voltage=0). Between the plates are rows of wires held at a voltage of typically -40 000 volts. The power is obtained by transforming ordinary alternating current to a high voltage and then rectifying it through some kind of solid-state rectifier On the plates the particles lose their charge and adhere to each other and the plate, forming a cake
Figure 9.2 shows in simplified form a wire-andplate ESP with two plates. The gas passes between the plates, which are electrically grounded (i.e., voltage = 0). Between the plates are rows of wires, held at a voltage of typically -40 000 volts. The power is obtained by transforming ordinary alternating current to a high voltage and then rectifying it through some kind of solid-state rectifier. On the plates the particles lose their charge and adhere to each other and the plate, forming a "cake
Solid cakes are removed by rapping the plates at regular time intervals with a mechanical or electromagnetic rapper that strikes a vertical or horizontal blow on the edge of the plate
Solid cakes are removed by rapping the plates at regular time intervals with a mechanical or electromagnetic rapper that strikes a vertical or horizontal blow on the edge of the plate
Some of the cake is always re-entrained thereby lowering the wastegas flowrate whereas enhancing the removal efficiency of the system If the collected particles are liquid, e.g., sulfuric acid mist, they run down the plate and drip off
Some of the cake is always re-entrained, thereby lowering the wastegas flowrate whereas enhancing the removal efficiency of the system. If the collected particles are liquid, e.g., sulfuric acid mist, they run down the plate and drip off
9.2 DIVIDING COLLECTION DEVICES Filters and scrubbers divide the flow into smaller parts where they can collect the particles Two types of filters, surface filters and depth filters, are commonly used in air pollution control
9.2 DIVIDING COLLECTION DEVICES Filters and scrubbers divide the flow into smaller parts where they can collect the particles. Two types of filters, surface filters and depth filters, are commonly used in air pollution control
