VEL ENGINEERING SERVICES

3 – A, Majithia Industrial Estate,

Waman Tukaram Patil Marg, Deonar,

Mumbai – 400 088.

Phone : 2556 5478, 25569122, 2558323

Fax : 2557 6395 e-mail vel4@vsnl.com

Website:http://www.velengineering.com

• Cement Mills,

• Grate Coolers ,

• Down Comer Duct,

• Gas Conditioning Towers ,

• Deep Pan Conveyors,

• Belt Conveyors etc ,

• Dust Suppression System at dump hoppers,

• Transfer points of belt conveyors, coal piles etc

MANUFACTURER’S OF WATER SPRAY SYSTEMS

Dust Suppression Systems

Introduction

Process and fugitive dust emissions are regulated pollutants that degrade the environment and endanger the health of workers exposed. Fugitive dust is a problem common to many industries. Some of these industries include mining, mineral and chemical processing, wood product, power generation and cement. Designers and operators within these industries find the control of fugitive dust from material handling systems. (dumping, conveying, screening, crushing, and storing) to be a topic of concern and interest. The creation of dust is an unavoidable result of such operations.

The Dust Control Systems are meant to control/suppress the dust generated during such operations. Considering the cost of a regulatory fine and the enhanced work environment that may be created, dust control becomes an investment in safe operations.

Choosing a strategy that best suits a given application point is the challenge facing the designers/manufacturers of dust control systems. An effective system for the control of fugitive dust in industry should meet the following objectives. 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. 5. No adverse effects on product quality or plant and machinery should be created.

Technologies available to control dust have their own set of implications for permitting dust load, capital cost, production, operating cost, and maintenance and are broadly classified as

i) DUST COLLECTION SYSTEMS

ii) DUST SUPPRESSION SYSTEMS

..

DUST COLLECTION SYSTEMS Ventilation Systems: When control of respirable dust is required or the material handled cannot tolerate the addition of moisture, a well-designed ventilation system may be in order. These systems extract the dust as it is created and filters it through conventional collectors such as fabric filters or scrubbers. Ventilation systems are highly effective for certain types of materials and applications

They are generally more expensive and power consumptive than the alternatives though they often may be the only alternative because of their highly rated efficiency. Dry collection systems are very efficient. However, this technology is capital intensive, high maintenance, and applicable only to sources that can be enclosed. Filter fabrics have limitations with stacking materials in a pile and the disposal of filters \ fabrics often produce secondary emissions. The means of reintroducing collected dust into sellable product is challenging, combined with the cost to replace and dispose filters.

DUST SUPPRESSION SYSTEMS

Water spray systems remain the most efficient and cost effective means of dust control for both process and fugitive dust emissions. Reason; the dust remains with the product of origin, while it is being disturbed. This process attempts to wet the material handled so that dust is bound to the surface of larger material and not released to the atmosphere. These systems are effective on most kinds of materials and applications.

Wet Chemical Systems: These systems utilize a wetting agent combined with water. Surfactants or other forms of bonding agents, further enhance the bonding characteristics of dust particles. These agents, combined with water, are available to match the chemistries of the particulate matter being addressed. They may not be applicable when the chemicals effect production. There are however, a number of suitable surfactant chemicals.

Agglomerative Dust Control :

Agglomerative dust suppression works on the principal that small particles of water will "come together” with small particles of solid matter (dust), forming larger and heavier particles that will settle by gravity. It uses water and no chemicals but it doesn't saturate the material; and it separates dust by the filtration process created from the fog. The performance of the agglomerative dust control is based upon the principal of agglomeration.

Dust particles released from the material being handled (i.e., conveyer points, screens, above and below crushers, and dump areas) are exposed to an environment that contains massive quantities of very fine water particles. The dust particles agglomerate with the water particles, increasing in weight, then falling back to their source of origin. The percentage of water added to the material is extremely low because only the fugitive dust is effected. The control efficiency of the system can be in excess of 95% depending on the application.

When the source of dust is hot, the fog evaporates to steam, generally not a good application for agglomerative dust technology. Agglomerative dust control is not appropriate for cement batch plants because the agglomerated dust sticks to the walls forming cement.

In certain applications, the fogging process will reduce visibility while agglomerating dust particles.

High pressure Atomizing System : To Achieve Fine Atomization High pressure nozzle with pressure in excess of 50 or even 300 bar is used. But it shows high wear rates and high. Installation cost. Here normally no special wetting agents or additives are needed.

Foam Dust Suppression System : Foam dust suppression system spray uses different spray header design and configuration based on the application. The high pressure foam agent penetrates to the dust particles. This Foam bubbles have a much larger surface area for capturing dust particlesIt uses an unique multicomponent concentrated foaming agents.

Fog Dust Suppression System:

Water is electrodynamically treated & then atomized into a mist of microscopic particles. This droplets join with airborne dust, increasing in weight so the combined particles settle back into the main material stream. This operates with out compressed air or chemical additives. It adds only minimal water to avoid material degradation.

Ultrasonic dust suppression systems: This system uses water and compressed 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. These are as follows. 1. Air compressor units.

2. Spray headers with pipe lines & pumping

system.

3. Control units with electrical systems.

The consumption of air per nozzle is 5 to 12 Nm3/hr in an over pressure range of 2-4 bar

The Ultrasonic Atomizing System generates droplets averaging 10 micron in size and is capable of suppressing sub-micron dust particles. 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 increased from the spatial probability, implying the need for fewer water droplets to ensure the desired efficiency. The Ultrasonic Atomizing Nozzle 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 is not prone to blockage. The advantages of using Ultrasonic Atomizing Systems for dust suppression can therefore be summaries as follows.

• Reduced Health Hazards.

• Decrease in Atmospheric Pollution.

• Improved Working Conditions

• Minimum Use of Water.

SYSTEM DESCRIPTION OF WATER SPRAY DUST SUPPRESSION SYSTEMS:

Normally the 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. Proportioned 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 dosed 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 used to supply pressurized water to spray headers. The required quantities of nozzles are used to spray water. Control units with electrical systems consists of sensing units, control panels. Coal flow is sensed by sensor.

Efficiency :

The efficiency of spray dust capture will increase by increasing the probability of water droplet and respirable dust particle contact.

It is increased 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. 3. Improving water droplet and dust particle interaction depends upon spray nozzle technologies. Factors affecting the efficiency of water-droplet formation are Particle size, Particle solubility, Presence of hygroscopic salts, Charge, Temperature, Relative humidity, Pressure, Electric Fields, wetability.

ENCLOSURES : For maximum efficiency of dust control systems, the dust source should be enclosed to provide protection from ambient conditions, especially wind.

In an exposed windy area, the fog and dust particles are dispersed preventing settlement of fugitive dust. These enclosures will vary from project to project but can be generally defined as follows:

Transfer points. At transfer points, enclosures should include;

a head box with inlet strip curtain; a seal of some type on the underside of the

feeder belt; a tight chute with a rock box (if the vertical drop

is substantial);

a cover over the receiving belt extending at least three belt widths downstream from the chute discharge and having a height at least equal to the belt width; and

a cover extending back on the receiving belt behind the chute approximately one belt width. In addition, tight skirt boards are necessary for the entire length of the belt cover. Special skirt board designs are available and should be utilized if the material handled is extremely dusty. This is especially true if the vertical fall is great, or if the belt speeds are high. Strip curtains should be fitted at the front and back discharges of the cover.

Screens. Screens may either be totally enclosed or open above the deck. If the screen is open, the feeder belt(s) should be enclosed with a head box that extends out over the deck and distribution plate to provide a protected area for dust suppression. The area between the deck and the hopper should be sealed with rubber. Over chutes can generally be open but their receiving belts must also be treated as a transfer point.

Crushers. Depending on the type of crusher and the material being crushed, the enclosure size will vary. In general, a rock box or vault under the crusher with substantial empty volume is desirable. If no vault is provided, the receiving belt must be tightly skirted.

The belt covers at least twice the size of a typical transfer point, and special skirting is preferred in the impact zone enclosing the belt. The mouth of the crusher should be protected in some way from wind so the belt, chute, or feeder supplying the crusher is "enclosed" with the crusher. A wind screen is generally sufficient.

Dump pockets and hoppers. Depending on the type of vehicles feeding a dump pocket or hopper; the mass flow through them; the nature of the material; operating procedures; and ambient conditions; enclosures for this application require custom designs..

In some cases, walls on three sides extending six feet or more above the maximum level of the material is all that is required. In other cases, a building with large dimensions and flexible or removable walls may be necessary. Each case will require individual design and fabrication. Many times the top of a hopper is much larger than necessary and can be covered with a solid sheet of material or tarp fabric similar to that used for dump trucks. Surround the point with wind fence material as much as possible to reduce the influence of ambient winds on the fog filter. Try to control the flow direction of the displaced air that carries the dust so that is stays within the enclosure. This requires some creativity but the principal is simple. Baffles or turning veins are often helpful.

VEL ENGINEERING SERVICES, Mumbai – 400 088

VEL ENGINEERING SERVICES, Mumbai – 400 088

VEL ENGINEERING SERVICES, Mumbai – 400 088