Molasses Filtration using a Putsch Filter Press

Eric Ekern Monitor Sugar Company

2600 S. Euclid Ave. Bay City, MI 48706

In preparation for the molasses desugarization project, Monitor Sugar installed a thin juice softening system in 1998 and began producing soft molasses. The following year the desugarization plant was completed and began processing the soft molasses stored from that previous campaign.

In order to extend the operating season for the desugarization plant, the plant needed the flexibility to process purchased molasses. Recognizing that molasses available to purchase would be hard molasses, a chemical softening plant was also built. In this operation, molasses is softened by adding soda ash and caustic to precipitate the calcium. A Putsch filter press was installed to filter the precipitate out of the molasses before sending it to the desugarization plant. Using a filter press provided the ability to sweeten off the filter cake and to produce a dry cake for easy disposal. Having no experience with a filter press in this application, the design provided for the filtered molasses to go to the Industrial filters already in use filtering soft molasses. The Industrial filters could then serve as polish filters to ensure that sediment that passed through the filter press did not reach the separation resin.

In the Spring of 200 1, the Chemical softening operation was put into service. Using the Putsch filter and the Industrial filters for polishing proved successful. The Putsch was able to provide the full flow of molasses to desugarization, which normally required two Industrials on-line, and the molasses was clean enough that the Industrials were lasting 10 times longer than they did on soft molasses. What was important at this point was that the Putsch did work in this application.

The natural extension of this success was to find a way to increase the utilization of the filter press. The operation of the desugarization plant during the intercampaign showed a load going to our water treatment system from washing the Industrial filters. We envisioned running the filter sluice through the Putsch press to save the residual molasses being lost to the ponds. With some minor piping changes we were able to route the sluice to the Putsch and recover the filtrate for molasses dilution. This process was tested in the Fall of2001. Tills filter was designed for precoat and bodyfeed operation, the same as the pressure leaf filters , but it requires enough throughput to fill the frames in order to produce a dry cake. Filtering the sluice proved to be a challenge. After all, we were trying to filter the material that had fouled the pressure leaf filters. The results were widely varying throughputs and as a result, inconsistent cake production. The solids in the cake were mostly filteraid and the cake was too light to drop off the cloths. It was also so porous that we did not have enough compressed air to dry the cake below about 70% moisture to help it drop from the cloths. The good news was the sugar recovery. The cake was 0.9% sugar, meaning we had reduced our filtration loss from about 500 pounds of sugar per filter cycle to about 20 pounds . The added benefit was that none of the material was going into our waste water system. Just avoiding the filteraid entering the ponds amounts to almost one ton a day that later has to be dredged from the ponds.

301

Molasses Filtration using a Putsch Filter Press

The next test was to see if soft molasses could be directly filtered. This would relieve the load on the Industrial filters and thus avoid the sugar loss and waste water loading. The Putsch filter was able to provide the full flow of molasses, equal to two Industrial filters, for about 6 hours, and then some make-up was run through the Industrials while the Putsch went through a cleaning cycle. This mode saved at least four sluices per day from the Industrial filters. Based on the sugar concentration in the sluice, which calculates to 500 pounds of sugar per sluice, we saved at least 2000 pounds of sugar a day.

Pleased with the apparent benefits, the final measure would be to see if the projected savings would actually be demonstrated in the sugar recovery reported for the desugarization plant. Graph I shows that the period where sluice was filtered had 2.2% better recovery than the preceding period and 2.0% better than the follow-up period. The molasses filtration test period measured 2.8% more recovery than the preceding control period.

The molasses recovered was a direct reduction in the load on our wastewater system. We were interested to see if this would show in the COD analysis. Graph II shows COD in the plant effluent did decrease, but there was an overall downward trend even when the Putsch was off line later in the campaign, so we cannot credit the improvement to the filter operation. Therefore, it is apparent that the load from desugarization is small when mixed with the total factory load during campaign. However it is easy to appreciate the intrinsic benefits of reduced flow, color, and insoluble solids into the factory ponds.

In overall performance, the Putsch filter proved to be a reliable improvement for our desugarization process, providing economic and operating benefits. By relieving the load on the Industrial filters, less of the control room operator's time is used attending to filter operation. During the 2002-2003 campaign, the filter press has been used for molasses filtration and continues to provide dependable service.

302

Molasses Filtration using a Putsch Filter Press

GRAPH I

AVERAGE RECOVERY

100

95

90 I:: -(l) e 85 (l) a.

80 , _ '~

75 1 - ­

70

baseline 1 sluice baseline 2 molasses

303

Molasses Filtration using a Putsch Filter Press

GRAPH II

EFFLUENT COD

8000

Putsch off Sluice Putsch off Molasses

'" 7800

7600

7400 I 7200

7000

... . __.. _-_.. _.

___. I ~COD I

6800

6600

6400 -

6200

304