Patent Application
20080087397
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According to the present invention, a cleaning chemical is forced through the high pressure needle nozzles 14 as paper is being manufactured. However, the chemicals are introduced on an intermittent basis.
As discussed above, the needle showers produce a very small, approximately 0.04 inch diameter, spray of water at a very high pressure, generally 150 to 250 psi, directly against the felt. Typically, the oscillating needle showers include a series of the needle nozzles spaced 3 inches to 6 inches apart, each with a 0.04 inch spray diameter. Thus, at any one time, the needle shower contacts only a small portion of the felt. Therefore, the nozzles are oscillated back and forth as the felt moves. Over a period of time, which depends upon the speed of the felt and the speed of the oscillation, the entire felt will be uniformly contacted with the spray from the needle showers. This period of time is referred to hereinafter as the full coverage period.
The needle showers themselves are operated continuously during the entire period of time that paper is being manufactured. Therefore, any time that the felt is moving, the needle showers should be applying the high pressure spray of material against the felt, and should be oscillating back and forth to ensure full coverage.
A cleaning solution is added intermittently through the needle showers as paper is being manufactured. The cleaning solution must be injected through the nozzles for a period of time at least equal to the full coverage period, and, preferably, for twice the full coverage period. This ensures that the entire felt is contacted with the cleaning solution. Subsequent to this period of time, the addition of the cleaning solution through the needle shower is discontinued. However, the papermaking process and the application of water without cleaning solution through the needle nozzle continues.
The actual duration of the full coverage period depends upon the felt rotation speed so as to achieve full coverage with the oscillating needle shower (the stroke timed to speed matching of the felt rpm per 0.040 inches movement). For a four felted machine at higher operating speeds, i.e., 3000-3600 fpm, the cleaning solution feed is on for about 15 minutes maximum each hour. This provides for double full coverage.
For a three-felted machine at the same speed, 20 minutes per hour is sufficient. For slower speeds, i.e., 2200-2800 fpm, 24 minutes of treatment each hour is optimal Generally, the minimum off time between cleaning applications will be at least one full coverage period. The inactive time, i.e., the period of time between cleaning times, should be no longer than 50 minutes. If the period of time between cleaning is too long, too much soil will fill the felt. Applying the cleaning chemical operation at least once per hour causes a cumulative effect on the felt providing significant cleaning for the felt.
The cleaning solution used in the present invention can be any cleaning solution typically employed to clean papermaking felt. Depending upon the chemistry of the particular equipment, these cleaning compositions can be alkaline, acid, anionic, or nonionic. Therefore, one will select one or more cleaning compositions, based on the particular papermaking operation. Generally, they will include, in addition to surfactants and the requisite acid or base wetting agents, chelants and sequestrants. Exemplary formulations for both acid and alkaline cleaning compositions are set out below (parts by weight).
The chemical compositions are generally added at about 200 to 600 ppm on a 100% actives basis. The detergent compositions themselves, however, are generally diluted and are applied at about 15-20% actives.
Since the total amount of soil which is deposited within a press fabric is basically proportional to the felt area, and since all press fabrics on a given machine are the same width (differing by their length), then the amount of press felt cleaner for each press felt can optimally by applied in proportion to the fabric's length, to achieve the same degree of cleanliness. It is best to adjust the concentration of the detergent applied to each felt based upon relative length and soil loading, rather than adjusting detergent feed duration. If the detergent feed duration were varied proportionally in the following example, the coverage of the oscillating needed shower coverage would not result in uniform application of the cleaner. For instance, for a given tri-nip press on a fine paper machine, the Pickup, 1st bottom press, and 3rd top press felts all have a width of 320″, and the following lengths respectively: 76′, 55.5′ and 46 feet. Thus, in proportion to their area, the press felts would be allocated approximately: 43%, 31% and 26% respectively, of the daily detergent allotment.
In a preferred embodiment, two different cleaning agents are applied alternately with spaced time intervals between the applications. As shown in
The invention will be further appreciated in light of the following example.
A test was performed on a fine paper machine equipped with a Twin-ver press, plus straight-through 3rd press and smoothing press, which produced light and medium basis weight free sheet paper grades. Previously, this machine had attempted to enact soils prevention by use of a cleaner continuously, through the high-pressure showers, with insufficient results. As a result, downtime cleaning of the press fabrics (no paper being manufactured on the reel) was required with an alkaline detergent. This not only caused loss of paper production, but also led to culled production during manufacturing, due to sheet defects that occurred in between the intervals of downtime washing events. These defects, i.e., corrugations, wrinkles, and ridges were caused by variation in cross-direction (CD) moisture content of the sheet. This was caused by soiling of the press felts, and due to the fact that no “on-the-run” felt washing capability was available to correct the problem. Additionally, no machine moisture adjustments were available other than dry weight headbox control.
The test consisted of application of alternating two cleaning compounds through the high pressure showers of each press fabric at various frequencies and durations, and measuring the effects upon felt Uhle box vacuums, press filtrate de-watering rates, press felt water permeability profiles, press felt service life, sheet quality, and machine runnability and up-time. The best results were observed when an acid and alkaline cleaner were alternated every other hour, at the rate of 24 minutes on and 36 minutes off, each hour (12 feed cycles each, per day), at a concentration in the range of 0.12-0.15%. This novel cleaning program resulted in huge improvements to the paper machine's production and quality yield, buy lowering CD sheet moisture variation (improvement in reel-shape, and fewer sheet breaks during felt washing). The overall results of the new cleaning program were as follows:
The trial machine monthly total losses for wrinkles were reduced to 19.1 Tons during the 4-month trial period, from 58.2 Tons (pre-trial) and a monthly average of 54.3 tons. Annualized this would result in a reduction of cull loss for wrinkles of 469.2 Tons.
The trial machine monthly total losses for ridges was reduced to 7.8 Tons during the 4 month trial period, from 71.1 Tons (Pre-trial) and a monthly average of 34.8 tons. Annualized this would result in a reduction of cull losses for ridges of 759.6 Tons.
The trial machine monthly total losses for corrugations was reduced to 41.5 Tons during the 4-month trial period, from 65.6 Tons (Pre-trial) and a monthly average of 38.8 tons. Annualized this would result in a reduction in culls for corrugations of 289.2 Tons.
The sum total of estimated reductions in annual culls for ridges, wrinkles and corrugations is 1,518 Tons for this trial machine.
Total cull losses for ridges, wrinkles, and corrugations on the trial machine's winder and super calendar were substantially lower in almost every category, during the trial period.
The present invention, when compared to standard cleaning methods, provided significant improvement in water permeability of the press fabric over its entire service life. There was, further, a significant reduction in the vacuum as measured at the UHLE box.
Further, alternating alkaline and acidic cleaners utilizing the method of the present invention further provided significantly improved results versus using only alkaline or only acidic cleaners. Hence, alternating cleaning chemistry types can increase felt void volume and improve felt dewatering performance over the useful life of the felt.
Further, due to the fact that the present invention uses relatively low concentration of cleaning solution, generally around 0.2 percent, whereas a standard cleaner might be used at a much higher rate, such as 3 percent, has relatively no impact on paper quality. Thus, the cleaning can be conducted while paper is being manufactured without causing sheet defects or sheet breaks. Further, since a relatively small amount of cleaning is applied, there is minimal impact on the cost of the paper. Further, the cost in chemicals is significantly less than the expense occurred in down time required to clean the felt off line.
This has been a description of the present invention along with the preferred method of practicing the invention. However, the invention itself should only be defined by the appended claims.
