Failure Of Dust Suppression Systems
At Coal Handling Plants Of蜀道难翻译
Thermal Power Stations
- A Ca Study -
By Makarand Joshi
1.0 Abstract: -
Many thermal power plants u coal as their fuel. To handle the coal, each power station is equipped with a coal handling plant. The coal has to be sized, procesd, and handled which should be done effectively and efficiently. While working in the coal handling plant the major factor which reduces staff efficiency is the working a dusty atmosphere. Lots of care is always taken to reduce dust emission.
Generally all systems ud in power station coal handling plants are wet dust suppression systems. In this paper the reasons for failure of the type of dust suppression system are discusd. The remedy
for the improvement of this system is also given in this paper. The existing system can be easily modified by using ultrasonic system. The spray discharge should be proportional with dust emission. The solenoid valve should be open with proportion with quantity of dust generation. The possibility of such type of this system is discusd in this paper.
2.0 Introduction: -
The Dust Suppression System is meant to suppress the coal dust generated during transfer of coal at feed/discharge points of conveyors in various transfer towers. There are veral existing methods of controlling dust but many are ineffective, costly and have detrimental effects on plant and machinery. An effective system for the control of fugitive dust in industry should meet the following objectives.
整理英语1. Must be efficient to meet Health & Safety requirements.
2. Be practical and simple in operation.
3. Have low initial cost.
4. Have low operating costs.
tomb sweeping day5. No adver effects on product quality or plant and machinery should be created.
But the system ud in the plant is not meeting the entire requirement, especially it does not meet Health & Safety requirements.
2.0 Existing dust suppression system: -
The existing dust suppression system in the coal handling plant is a wet dust suppression system. Wetting Agents are chemicals that are added to water to improve the rate at which spray droplets wet dust particles.
This system consists of three main parts.
1. Proportioner units.
2. Spray headers with pipe lines & pumping system.
3. Control units with electrical systems.
PROPORTIONER UNITS include feed water pump, metering pump, feed water tank, solutions tanks.
The water required for the system is supply by feed water pump. Wetting agent, which is in liquid condition, is dod by metering pump as per requirement.
SPRAY HEADERS WITH PIPE LINES PUMPING SYSTEM includes solution pumps, isolating valves, spray nozzles, and pipe lines. The solution pumps are ud to supply pressurized water to spray headers. The required quantities of nozzles are ud to spray water.
CONTROL UNITS WITH ELECTRICAL SYSTEMS consists of nsing units, control panels. Coal flow is n by nsor. The control panels are consisting of various relays and transformer.
3.1 Operating principles of existing system: -
Auto control or manual control governs the system. It has to be insured that main tank is filled with water. The water is pumped by feed water pump from main tank to feed water tank and at the same time metering pump dos proper quantity of chemical. The feed water pump operation is controlled by float switch automatically. The pump picks up at low level and stopped at high level. The interlock with low level of main tank will not allow to pickup the feed water pump.
初步英文The metering pump will stop the operation by nsing low chemicals in tank. After insuring proper lev
el the solution pumps will start. If the pressure increa the pressure relief valve keeps the system in recalculation.
The nsing system for controlling spray at proper header ensures spraying solution if conveyor is running with coal. And will not allow spraying solution if conveyors are running empty. (See Figure No 1)
The solenoid valve headers are energized if conveyor is running with coal. If all or some of the solenoid valves are not energized the system will realize pressure through pressure relief valve, which protects the system. A solenoid valve is provided with bypass line, which operates when none of the spray header solenoid valves are operative.
Recalculation
if belts are off of solution tank level
belt running with coal
Figure No 1
3.2 Existing system draw back: -
This system does not effective on respirable dust. Typical water droplet sizes are 200 to 600 microns, which are much greater than the respirable dust. And it does not operate on the emission quantity. The spray of the system should be operated on emission quantity. Thus, water sprays can be improved by increasing pressure or by designing nozzles which produce smaller droplets. And also developing the control system which n quantity of dust. Most of the improvements in this direction already have been made. The problem with this approach, and one, which prevents much additional improvement, is that introduction of very small water droplets into an atmosphere.
4.0 Efficiency of system: -
Over the years, water sprays has established the following facts:
1. For a given spray nozzle, the collection efficiency for small dust particles increas as
the pressure increas
2. At a given pressure, the efficiency increas as the nozzle design is changed so as to
produce smaller droplets.
The conclusion is clear, the smaller droplets [1] are more effective in knocking small dust particles out of the air. The reason for this is not hard to e. Consider a water droplet about to impinge on a dust particle, or what is aerodynamically equivalent, a dust particle about to impinge on a water droplet, as shown in the Fig No 2. If the droplet diameter is much greater than the dust particle, the dust particle simply follows the airstrip lines around the droplet, and little or no contact occurs. If, the water droplet is of a size that is comparable to that of the dust particle, contact occurs as the dust particle tries to follow the streamlines. Thus the probability of impact increas as the size of the water spray droplets decreas.
4.1 Efficiency of water-droplet formation: -
Factors affecting the efficiency of water-droplet formation are Particle size, Particle solubility, Particle (Hydrophobic or hydrophilic), Prence of hygroscopic salts, Charge, Temperature, Relative humidity, Pressure, Electric Fields, wettability.
The efficiency of spray dust capture will increa [2] by increasing the probability of water droplet and respirable dust particle contact.
It is incread by
1. Increasing the number of smaller sized spray droplets per unit volume of water
utilized
2. Optimizing the energy transfer of spray droplets with the dust-laden air. Improving
water droplet and dust particle interaction depends upon [3]spray nozzle technologies.
bowl是什么意思
DUST PARTICLE IMPACT AIR SMALL DROPLET
SMALL DROPLET IS OF USE LARGE DROPLET OF NO USE Figure No 2
5.0 Ultrasonic dust suppression systems: -
This system us water and compresd air to produce micron sized droplets that are able to suppress respirable dust without adding any detectable moisture to the process. Ideal for spray curtains to contain dust within hoppers. Generally the system consists of three main parts. The are as follows.
1. Air compressor units.
2. Spray headers with pipe lines & pumping system.
3. Control units with electrical systems.
5.1 Operating theory: -
The theory behind the Ultrasonic Atomizing System is bad on rearch considering a water droplet from a spray that is about to impinge on a dust particle. The probability of impaction increas as the size of the water spray droplet decreas. This explains why conventional hydraulic water sprays are not effective on respirable dust. With typical diameters of 200-600 microns the droplets are much larger than the dusts they are attempting to suppress.
The Ultrasonic Atomizing System generates droplets averaging 10 micron in size and is capable of suppressing sub-micron dust particles. In addition to this particle size theory, the results of additional rearch indicate there is another significant phenomenon that occurs when Ultrasonic Atomizing Systems are applied to dust suppression. The effect can be compared to an electrostatic precipitator in which dust particles are charged and then collected on plates of opposite charge. It was found that
dust particles generally carry certain negative potential depending on the nature of the dust and the ambient
conditions. Water droplets produced by the nozzles carry a charge that is strongly positive in relation to the dust particles.
The result is that the probability of collision between a droplet and particle is greatly incread from the spatial probability, implying the need for fewer water droplets to ensure the desired efficiency.
If the diameter of the droplet is much greater than the dust particle then the dust particle simply follows the air streamlines around the droplet and little or no contact occurs. If, on the other hand, the water droplet is of a comparable size to the dust particle then contact occurs as the dust particle tries to follow the air streamline.Thus, a nozzle generating a den fog of 1-10 micron size droplets can be ud to envelop and smother dust particles at their source and prevent them from becoming airborne.
5.2 Design: -
The Ultrasonic Atomizing Nozzle takes the form of a whistle using compresd air which accelerates
through a converge ction and expands to a diverge ction into a resonator chamber. This produces a powerful sonic shockwave. Water or other liquids delivered to this sonic area are shattered into droplets. Droplets produced by sonic atomization are small and relatively uniform in size, in the order of 10 micron, with a Low Mass and low forward velocity. The nozzles have a large liquid port which are not prone to blockage.
5.3 Advantages: -
The advantages of using Ultrasonic Atomizing Systems for dust suppression can therefore be summaries as follows.
• Reduced Health Hazards.
• Decrea in Atmospheric Pollution.
• Improved Working Conditions
wooyun org• Efficient Operation with Minimum U of Water. Thus Not Saturating the Product or Plant and Equipment.
他们的英语5.4 Design of nozzles: -委托书英文
The Design of [4] the system is bad on a very unique device which can produce a very den fog of 1 - 10 micron size water droplets which literally blanket the dust source and keep the dust particles from becoming airborne. It does this at low cost, both from a capital and a maintenance standpoint, while achieving all of the goals stated above for an ideal dust suppression system.The fogger [4] is an air driven acoustic oscillator for fogging liquids by passing them through a field of high frequency sound waves. This is accomplished by compressing air upstream of a specially designed converge ction of the fogger. To further enhance the fogging capabilities, a resonating chamber in the path of the air stream reflects the air stream back at itlf to amplify and complement the primary shock wave.
Once this standing shock wave [4] is generated, water is delivered through annular orifices where it is first sheared into relatively small droplets. The small droplets are then carried by the primary air stream into the inten shock wave where the sound energy is converted into work by exploding the droplets into thousands of micron size droplets. After having done its work, the air then escapes around the resonating chamber and carries the droplets downstream in a soft, low velocity fog. (See Figure No 3).The design of this fogger has obvious benefits regarding the control of respirable dust.
6.0 Devices for the measurement and characterization: -.
Devices for the measurement and characterization of respirable dusts matter are needed to asss worker exposure to the health hazards and to evaluate control technologies. There are various types of devices.
6.1 Device bad on the light-scattering properties: -
When airborne dusts or suspended particulate are irradiated with light, the light is scattered in all directions. The intensity of light scattered at any particular angle depends on the wavelength [5] of the light and the size, volatility, and mass concentration of the dust or suspended particles. Both theory and experiment indicate that at a scattering angle of around 200 to 300, the size and volatility of respirable coal dusts have a negligible impact on the measured intensity so that this intensity is directly proportional to the mass concentration of the dust. At an angle of 150, equal concentrations of either respirable coal dust or diel particulate matter (DPM) yield equal intensities of scattered light. At larger angles, the intensities from DPM are significantly greater. (See Fig No 4) The results, while tentative, imply that devices that measure light-scattering signatures at one or more specific angles in the range of 150 to 300 offer significant promi for respirable dust or DPM measurement and, possibly, for determination of mass fractions of dust/DPM mixtures. As this basic rearch project progress, the implications will be explored in greater detail.
Reflected air
oneyearstream绯闻女孩第6季
Compresd air
Figure No 3
