Membrane Pressure Cavity Filter Resultant Lower Moisture and Sugar Retention

Transcription

1 Membrane Pressure Cavity Filter Resultant Lower Moisture and Sugar Retention E. Lynn Powers and Gary L. Larson, P.O. Box 700, Torrington Wyoming Transportation of Precipitated Calcium Carbonate (P.C.c.) has historically been in the form ofa slurry called Lime Flume. The 1993 campaign was a transition year when sludge off the rotary vacuum filters was hauled with four, two ton dump trucks. It must be noted that the moisture content of this sludge was approximately 50% and the initial spray on the rotary vacuum filters was shut off in order to meet this parameter. This practice increased sugar loss in the cake. In 1994 two Putsch Membrane Filters were installed at the Torrington factory, enabling the entire daily production of approximately 400 tons of P.C.C. to be hauled off at the rate of 10 to 12 tons per load with the use of a single Terex dump truck. Installation of two membrane filters at Torrington came about because a pro-active approach was taken on environmental issues, specifically ground water quality. Figure # e GIl 50 'c C -< I, Monitoring Well o. 2 Downgradient of Former PCC Ponds I I I t I I 00 0\ 0 f:') '<T '<T V) V) 'l) 'l) \ 0\ ;;, V) \D f:') 00 f:') t' t' t'!::' 'l) 'l) 'l) t:=:- V) 0 Date Sampled Table Figure #1 Date I 12/6/ /13/89 12/6/ /90 6/25/ /91 6/26/ /23/ /93 Value Date 1118/94 4/28/94 6/24/94 10/12/ /95 4/11/95 7/24/95 2/12/96 5/11/96 7/9/96 10/22/96 Value II Figure #1 shows results from 1988 to 1996 of ammonia in the ground water samples taken from monitoring wed o. 2 directly down gradient offormer P.C.C. ponds. In January 1993 note the sudden drop in ammonia content and the gradual decline since the installation ofthe membrane filters. 159

2 Additional benefits that were realized include: 1. Solids content ofthe filter cake approximately 70% Figure #2 Lime Cake Crop Year Figure #2 shows moisture content for crop years 94, 95, and 96. The Torrington landfill permit requires that all P.c.c. going to landfill must pass the paint filter test. This is easily achieved with these moistures. 2. Low residual sugar concentration with the cake. s CD I) ED c o f!. o. Figure #3 Sugar Loss in Lime Cake Crop Year Figure #3 represents results of sugar loss in lime cake % on beets for crop years 92 through was the year that Torrington removed lime cake from the rotary vacuum filters in "dry" form. Results of the membrane filters are reflected in 94,95 and

3 3. Improvement in carbonation due to a higher quality filtrate and sweet water is reflected in lower flocculant usage. Figure #4 Flocculant Usage Year Campaign Ended Figure #4 illustrates flocculant usage based on cost per ton of beets. Cost reduction in 93 is attributed to a dry versus wet flocculant that was used in Continued reduction in 94, 95 and 96 is attributed to the membrane filters. The Putsch membrane pressure filter (PKF) is based on the principle of a chamber filter press which is additionally equipped with a press membrane. Figure #5 MEMBRAE PLAT E - WA S U W 4T ER PR E SSURE PLAT E As shown in Figure #5 the carbonated juice concentrate flows through a mud/sludge channel into individual filter chambers. Filtrate is drained through the bottom part of the filter plates. By moving a membrane in the direction of the fixed pressure plate during membrane plate pre-pressing the filter cake is compressed. 161,-

4 Figure # During Unstressed During membrane ftj tration squeeze Figure #6 is a side view of a membrane plate. umber 1 is the position ofdiaphragms at start of filling. Position number 2 is during filtration where chambers are filled up and filter cake presses diaphragms against the carrier plate. Position number 3 shows membrane during squeeze. The diaphragms are pressed against the filter cake by the squeeze pressure. Refer to Figure #5 Water enters the upper part of membrane plates during the process of sweetening off. Wash water penetrates the filter cloth of membrane plate then flows ilirectly through the filter cake in the direction of the pressure plate. The final solids content of approximately 70% can only be obtained by subsequent air drying. In contrast to drum filters, using membrane filters enables us to minimize sweet waters and thus, increases output of sugar. Saving sweetening off water reduces the dilution of the juice which means that there is less water to be evaporated, in turn lowering steam consumption. Welcome to Holly Sugar Corporation facility. These are the Putsch filters installed in 1994 at Torrington. This is the mud density transmitters. Water and mud flow transmitters not only control volume in a cycle but also record accumulation for the total run. Schematics indicate which step ofoperation the filter is in. Function timers control or monitor the following steps ofoperation. STEPS OF OPERATIO 1.) Filling: Mud pump is running in slow speed. Pre-coating of filter. 2.) Filtration: Mud pump is running at high speed. This step is controlled by the gallon counter, set at 800 gallons, then by flow meter which stops cycle when flow slows to set point. 3.) Pre-pressing: Pressing ofcake at 40 psi. 4.) Intermediate pressing: Pressing ofcake at 53 psi. 5.) Cake Washing: Sweetening offofcake. Time is controlled by water counter. 162

5 6.) Final pressing ofcake. 7.) Air drying ofcake. 8.) Emptying feed channel: Mud in feed channel is allowed to return to mud tarue 9.) Air drying of feed channel. lo.) Membrane Vent: Returns air in membrane plates to zero. This step is critical to assure membrane plates are not damaged. 11.) Start discharge screw, apron opens. 12.) Drop tail end cake. 13.) Wait: Screw will empty out. 14.) Drop head end cake. A 30 second delay exists between tail end dropping and head end opening. This is to assure screws are clear ofmud. Once the filter is closed, the apron shuts and its ready for another cycle. The following parameters must be met before the filter will start: A. 50% level in mud tank. B. Mud pump running. C. Wash water pump running. D. Air compressor running. E. A minimum of 11 5 psi pressure in cake drying air receiver. F. Another filter not filling. Clear plastic curtains are to protect from a blow-out of juice or air while filter is in operation, or in washing cycle. The filters are washed with 275 psi water sprays. The apron shuts and will direct water away from screws into drain. These filters are washed once every eight hours and one is acidized approximately every 15 days. Membrane plates and pressure plates are numbered in order to monitor cloth usage and performance. The instrument which controls the level and temperature of water to the filters is located at our main control panel on the beet end. A T erex truck is capable 0 f hauling 17 tons, making 12 to 13 trips to landfill per 8 hour shift. In summary the advantages ofthe Putsch filter are: 1. Reduced sugar losses - increasing profits.02% on beets is a considerable success. 2. Excellent quality filtrate and sweet water improving operations. 3. Reduced water consumption which in turn reduces fuel usage increasing profits. 4. o recirculation of filtrate improving carbonation. 5. Drier cake allows transportation ofp.c.c. to landfill. 163