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Tips to Keep Tunnels in Tune, on Time

Paul J. Rogers, P.E. |

The beauty of the tunnel washer is its ability to reuse water without an external system, and to reclaim heat and chemicals.
In a nutshell, soiled goods go in the front of the tunnel and are discharged clean. This works because the cleanest water is in the back of the tunnel. As goods move forward, they’re constantly in contact with the cleanest water.
Batch tunnel washers are available in a wide range of compartments and processing capacities. There are top- and bottom-transfer models, which both clean equally well. The only difference between these designs is the means through which goods are moved from one compartment to the next.
All batch tunnel washers are equal in the principles of operation. They are based on a balanced system that incorporates 1) time 2) temperature 3) mechanical agitation and 4) chemicals.
If an operator reduces time, he’ll need to increase one of the other three system components. Mechanical agitation is fixed in a batch tunnel washer; temperature has a limited effect. While each component is critical, time has the greatest impact in terms of chemical and water costs.
Say an operator tries to speed up production by raising the water level to rinse faster, for example. This will typically result in increased steam costs to heat that water back up in the wash zone, because it will not pick up as much heat from the goods in the rinse zone.
To minimize unwanted spikes in production costs, operators would be wise to balance the four basic components.CALCULATING LOAD SIZE
Manufacturers make tunnels with as few as five compartments or as many as 20. Standard capacities are 110 to 130 pounds per compartment, but models are also available in 55 to 200 pounds, if more or less capacity is needed.
There is a formula by which an operator can determine peak efficiency for any given tunnel operation.
If a 16-compartment tunnel operates for 24 minutes of “active” time, for example, the operator can divide the active time by the number of compartments to arrive at the minutes per compartment. In this case, that number is 1.5 minutes.
By dividing 60 minutes by the 1.5-minute compartment time, the operator learns that the tunnel processes 40 batches per hour.
Multiplying 40 batches by 110 pounds per batch, for example, yields a peak efficiency of 4,400 pounds per hour.
As a rule, an operator needs to allow for the same “active” or “bath” time as that of a traditional washer-extractor. Typically, this is a minimum of 24 minutes and accounts for the fills and drains between each cycle in a washer-extractor formula: eight minutes of break time, 10 minutes of suds time and another six minutes of rinse time.OPTIMIZING PERFORMANCE
A typical operator may process 4 to 8 million pounds per year (based on a single shift). In order to best minimize downtime from a production and maintenance standpoint, operators must:
• Provide a continuous flow of goods to the batch tunnel washer.
Managing route structure and balancing soil-sorting capacity are the keys to doing that.
• Provide a continuous flow of goods from the batch tunnel washer.
Ensuring sufficient staffing and training employees to move goods quickly and appropriately will help prevent the tunnel from going into a standby mode, thus minimizing production downtime.
• Properly classify goods to ensure continuous flow and peak efficiency.
Operators must manage the soil mix for quality and production flow (i.e. light, medium and heavy soil), and use caution when changing cycle times based on soil classification. All batches before and after will run on the longer cycle.
For example, if lightly soiled goods are run on a two-minute wash formula and then heavily soiled goods follow on a three-minute formula, every compartment in front of the heavily soiled goods will be washed for the longer period.
Therefore, if using a 16-compartment tunnel, an operator stands to lose one minute on each of the previous 15 compartments (translating to 15 minutes of lost production time) and on each of the 15 compartments following the last (another 15 minutes).
When managing soil flow, it’s generally not necessary to leave pockets empty between batches. But, if mixing dark colors that have a tendency to bleed, an operator should leave a few empty compartments between goods, because dumping all of the water out of the tunnel eliminates the efficiency that is expected.
Finally, managing the flow of full-dry items can keep things rolling. To avoid having a tunnel go into standby mode if there is not enough drying capacity, an operator should vary the flow of full-dry items with easier-to-dry or bypass items, such as sheets, that can go directly to the ironer after extraction.
These are some general guidelines to assist laundry operators in securing optimal performance from their batch tunnel washers.
 

About the author

Paul J. Rogers, P.E.

G.A. Braun

Engineering Manager

Paul J. Rogers, P.E., is engineering manager for G.A. Braun, Syracuse, N.Y.

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