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Automatic waste collection: an environmental and economic waste management consideration.

Automatic Waste Collection: An Environmental and Economic Waste Management Consideration

Modern automatic central station vacuum waste collection systems can be of significant advantage in a nonwoven production operation. These systems meet environmental demands for a cleaner workplace and cleaner air. They also provide major improvements in product quality while offering economic advantages.

The problems of handling waste fiber, dust, lint and edge trim have had a progression of solutions according to the then available technology. In the past, labor pools were large and inexpensive and machinery was relatively slow. In addition, the fiber processed was comparatively low cost and there was no great concern for fiber reclamation, environmental quality or waste disposal.

These facts added up to a low priority for waste management and reclamation. However, in 1989 and into the foreseeable future, waste management is of vital concern in the entire textile processing industry and very definitely includes nonwoven plants.

Five System Options

The ideal solution to these problems is to efficiently collect waste wherever it is produced and convey it to a predetermined location(s) for disposal, direct reuse or reclamation. This function has generally been performed in one of five different ways, singly or in combination. These are manually, by fan, by mechanical methods (auger, conveyor), by portable vacuum or by central station vacuum systems.

Each of these methods has its special role. Defective fabric rolls and start-up strikeoffs, cardboard and large wastes can best be handled manually by cart. If a considerable amount of air volume must be moved to collect dusty air from a room or hood at a garnett or picker, or if flock needs to be collected from a shear ledger blade or a napper, a proper fan with a high air flow and relatively low air pressure is appropriate. Mechanical conveyors move bulk for short distances. Portable vacuum units are typically used for very small limited use applications.

Central vacuum waste collection systems offer unique solutions. These do not replace all other systems of waste collection, but operate as a useful adjunct.

Modern high speed machines are often directly linked to other machines in a production operation and a problem with one unit affects the entire line. The more machines linked and the higher the production line speed, the more costly the downtime. To stop a machine to manually clean out waste is expensive. If this waste is allowed to build up, for example, under a card or garnett, product contamination will result in lower product quality. Automatic timely collection of waste is an obvious advantage and automatic central station vacuum systems excel in this function.

Mechanical waste collection by auger or conveyor is useful in some areas but is limited to short distance transport situations.

Fans are essential in large air volume applications, but for most waste handling requirements they are not as efficient as a centrifugal exhauster for the same amount of work.

Fans cannot convey material long distances without the use of booster fans. Central vacuum systems can extend thousands of feet around a mill with no diminution of vacuum pressure. Fan systems tend to be sized for immediate requirements and not easily expanded. A properly designed central vacuum system is capable of extensive expansion.

Hoses and floor sweep stations are easily added to existing waste collection lines (headers) from the existing waste house. Automatic valves are generally controlled by programmable controllers that are easily expanded to accommodate additional automatic valves. A further advantage of a central vacuum system is that it is easier to protect from the risk of fire.

Automatic Central Vacuum Systems For Here And Now

An automatic central station vacuum collection system is comprised of a waste house and the vacuum inlets. The waste house is made up of a vacuum source, an automatically emptying waste receiver (primary separator), a fine dust filter (secondary separator) and a waste receptacle. The vacuum inlets are various hose stations and floor sweep stations placed around the machinery and automatic collection nozzles positioned throughout the plant at cleaners, openers, condensers, cards and filter bags.

The automatic discharge vacuum receiver (primary waste receiver) discharges collected waste into a baler, compactor or other waste receptacle. In general, this is a timed interval but, when the receiver is equipped with a level detector, the detector senses a full receiver load and interrupts the timed cycle for emptying. The timed cycle accommodates the normal automatic valve volume and the level detector overrides this during periods of high volume collection such as work shift change or increased manual cleaning.

"Central" refers to the location of the waste house with all vacuum inlets leading to it. It is generally located near a shipping dock to facilitate storage, handling and shipment of waste bales formed automatically by the waste baler. Bales are always the same size and weight.

A central station system can be considered by practically any nonwoven plant or other textile manufacturing operation regardless of size. A moderately sized typical waste house would consist of a centrifugal exhauster with a 60-100 HP motor, a fine dust filter with pulse jet bag cleaning and twin automatic waste receivers (to supply a constant vacuum) automatically emptying to a waste receptacle--compactor, baler, cart or feed bin. Automatic horizontal balers are the most useful waste receptacles and can be supplied according to requirement. Bales can be used for sale, disposal, storage for later use or for reclamation blending.

A centrifugal exhauster normally provides the most economical vacuum source. Once this type of pulp reaches its operating pressure level, increased amperage occurs with increased air volume, so the cost of using the system varies directly with the actual use of the system. The waste receiver collects the waste and automatically empties it directly to a waste receptacle for reuse or disposal. The dusty air passes through a separator screen to a secondary receiver or dust filter, where the dust is filtered from the air stream and manually or automatically collected for disposal. The clean air is then returned to the exhauster.

Automatic valves are placed on nozzles especially designed for each application and collect waste intermittently where it is being constantly collected by fan or free fall. When a vacuum inlet on a central vacuum system is opened to the atmosphere (valve opens), the result is a "vacuum implosion." This implosion draws waste into the small diameter conveying line with great force and transports this waste to the vacuum waste receiver with accelerated velocities exceeding 150 feet a second. The tube couplings must be sturdy and tightly sealed and the fittings must be designed for proper flow angles to minimize frictional losses.

Dust Free Collection

The system itself is designed to convey waste dust-free and it is self-cleaning in that the dust particles are separated from the dust laden air in the secondary separator so the exhausted air can be directed outdoors or even back into the mill. The temperature of the exhausted air is normally about 70 [degrees] F above the ambient temperature so some mills enjoy an economic advantage by returning heated air back to the mill during the winter months.

Negative room pressures cause air currents to occur that disturb dust particles and keep them in suspension. This contaminated air is unhealthy for employees, often affects their work attitude and can reduce product quality. Central vacuum systems operate with high pressure (six to 12 inch Hg) and low air volume (1500 CFM to 4000 CFM). Because only small quantities of air are removed, negative room pressures are not created.

Many plants clean machines and work areas with compressed air "blow downs." Clean, dry compressed air is costly and can be physically hazardous if not properly used. The judicious use of vacuum hoses and floor sweep stations can often eliminate the use of compressed air for cleaning purposes. This advantage of a central vacuum system can result in lower product contamination and improved employee safety.

Employee safety is also involved with environmental quality in other ways. Respirable air quality is the most obvious advantage of improved environmental quality. The use of automatic valves and the corresponding reduction in physical contact with dust avoids direct "prolonged" contact with potentially hazardous waste such as raw cotton dust, chemically treated fibers and bonding resins.

Automatic Filter Bags

Special filter bag sets with top and bottom valves for automatic simultaneous emptying and cleaning of the filter bag material are available commercially (Figure 1). When the filter bags are emptied one at a time by vacuum implosion, closing the top valve of the bag being emptied of waste causes a reverse air flow through the filter media and helps to keep it clean. These filter bags are typically used to collect lint and dust picked up by fan systems.

Filter bags let the air pass through and retain the lint, dust or waste fiber for automatic collection by the vacuum system. They are typically located adjacent to the machinery they serve, or at least in the same area so negative room pressure is not produced and smaller motors are required to power the collection fans. Because these filter bags are self cleaning and automatically emptied, over time they do not present increased back pressure to the fan.

The use of the automatic filter bags, therefore, contributes to both product and environmental quality. By eliminating the need to stop production equipment to empty these bags, downtime is reduced, output is increased and direct manual labor to empty filter bag socks, canisters or storage plenums is eliminated.

The Economic Advantages

Central station vacuum systems can automatically collect fiber waste and deposit it directly to reclamation systems. The selection of waste receiver type and of the screen separator used in the automatic waste receiver aids in the removal of fine dust from loose fiber before it is introduced to the reclamation equipment for further processing.

At the reclamation unit, low grade "trash" is picked up automatically by the vacuum system and deposited in the disposal receptacle, while the high grade reclaimed fiber is collected and conveyed to the high grade fiber receptacle. A modern waste collection can separately collect various grades of waste throughout a mill and deposit these wastes according to requirements (Figure 2).

Through the use of newly developed waste receivers and fine dust collection equipment, expensive resins used in the thermal bonding process can be salvaged for reuse. Some uncured and partially cured resin can be separated from the fiber waste for blending with new resin at air lay lines. In some cases the fiber can also be recycled. An additional advantage of this reclamation of fiber and resin is to improve environmental quality by handling this resin/fiber mixture by vacuum in a dust free system that will improve respirable air and avoid skin contact by plant personnel.

By separating wastes into high and low grade products there are many economic as well as environmental advantages. The environmental advantages are in producing less incinerator pollution and in slowing the rate of filling land-fills. Economically, fiber which is recycled or reclaimed is fiber that does not need to be repurchased; in addition, it is fiber that the mill does not have to pay to have trucked to a landfill or incinerator.

Special Nozzles For Automatic Collection

Mills cannot always schedule their production lots advantageously, so small and large lots may become mixed and certain colors or fibers from one lot would reduce product quality if mixed with the next. Two special vacuum systems that assist mills to effectively overcome this problem for those operating cards and garnetts are in operation in many plants today.

In the first instance, a nozzle is placed under the card or garnett or between the card and feed bin where fiber falls out. Vacuum implosion applied intermittently cleans the fiber from this area. Undercard cleaning is extremely effective when performed with vacuum implosion. Fan pressures are not sufficient to draw into the nozzle the mass of fiber that forms in this area. When the under card system is blocked, the air follows the path of least resistance and improves top card cleaning. When existing under card cleaning systems are replaced with vacuum cleaning, the top card cleaning is also improved.

The second system consists of a series of small nozzles packed at the shoulder of each worker and stripper cylinder to keep the fiber from migrating onto the journals and into the bearing. Aside from reducing cleanup time between lots, these nozzles also keep synthetic fiber from melting in the bearing. Fiber collected can be directly returned to the feed bin for re-use.

Automating Trim Collection

Handling continuous edge trim in a nonwoven production line is usually a manual operation. The continuous trim falls into a box or onto the floor and must be taken away at routine intervals. Some trim lines operate on the "fan" venturi principle to move the trim in a continuous ribbon to a collection point adjacent to the machine or nearby. Adding a chopper to cut the trim into pieces greatly increases the density of the collecting unit and increases the time between removing the collected trim containers.

When using a central vacuum system, the chopper can be inserted into the vacuum line at trim lines at various plant locations and the small cut pieces are picked up and conveyed 1000 feet or more by constant vacuum to a waste receptacle. This eliminates completely the manual labor to collect the trim while taking advantage of the increased density of the chopped trim to pack more compactly in the waste receptacle.

It is also possible with a central vacuum system to treat the edge trim like any other intermittent automatic valve situation. The chopper can be inserted in line with a venturi--or preferably a material handling fan--which would deposit the pieces in a funnel or filter bag for automatic cleaning.

Flexible Programmable Controls

In some mills there are hundreds of automatic valve waste collection positions. To further improve the usefulness of a central vacuum system, it is important to schedule certain valves to open at specific intervals. The use of programmable controllers (PLC) permits this flexibility.

Today's programmable controllers can be easily expanded or reprogrammed to suit the mill's waste requirements. A single PLC can control both the waste house functions as well as the mill's automatic valve requirements. Diagnostic units can pinpoint control problems and alert mill maintenance.

The PLC controls automatic valves. These valves are generally six and eight inches in diameter. Due to size and speed of these valves, the lack of need to "balance" air flows, and the use of installing conveying lines and vacuum systems with PLC controls are capable of much more flexibility than fan systems.

Some advantages of an automatic central station vacuum waste collection system are:

* A measurably cleaner mill environment

* Improved product quality

* Dollar saving through reduced machine downtime, reduced labor costs, lower health cost, lower health and fire insurance rates, low vacuum system operating cost, the ability to economically separate high and low grades of waste to reduce the amount of waste for disposal and to reclaim and reuse as much fiber as possible that has already been paid for.

There are already many useful applications of a high vacuum low (air) volume system. As new production machinery and conditions are developed, mills find new ways to further extend the usefulness of this vacuum system to meet these new situations. Special nozzles, newly-designed waste receivers, methods of handling fine dust and new concepts involving separation of waste grades and of waste reclamation are being developed constantly as the system is updated.

Industrial waste is more and more an area to be carefully controlled for a variety of reasons and plant management can use today's more sophisticated vacuum waste collection systems as an extremely useful tool in efficient mill operation. [Figure 2 Omitted]

PHOTO : Figure 1: Automatic filter bags are simultaneously cleaned and emptied in the vacuum waste

PHOTO : collection system.

JOHN COON Sales Engineer Abington, Inc. North Abington, MA
COPYRIGHT 1989 Rodman Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1989 Gale, Cengage Learning. All rights reserved.

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Author:Coon, John
Publication:Nonwovens Industry
Date:Oct 1, 1989
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