ECONOMIC ASPECTS OF RAW JUICE CHROMATOGRAPIDC PURIFICATION

Transcription

1 ECONOMIC ASPECTS OF RAW JUICE CHROMATOGRAPIDC PURIFICATION ABSTRACT Vadim Kochergin* and Bill Jacob Amalgamated Research Inc. P.O. Box 228 Twin Falls, Idaho The current status of the raw juice chromatographic process developed by Amalgamated Research Inc. is reviewed. While the sugar technologists are comfortable with most of the major steps of the process, the search for the best techniques to separate suspended solids from feed raw juice stream is still in progress. It appears from our economic analysis that the lime kiln replacement with membrane filtration may be feasible only if the overall process includes chromatographic separation. The feasibility of the new process is affected by many factors, such as location, environmental regulations, capacity and configuration of sugar end, presence ofjuice storage, etc. Various approaches are discussed allowing for the gradual integration of chromatographic purification ofraw beet juice into the existing plants. INTRODUCTION The raw beet/cane juice chromatographic purification process developed and patented by Amalgamated Research lnc.(ari) was first introduced several years agol.2j. Once implemented, the process will eliminate the use of lime and drastically increase the non-sugar elimination across the beet-end. Use of chromatographic purification on the front end of the sugar factory allows one to achieve higher purity syrups, which simplifies the sugar end operation. The purpose of the present paper is to provide an update on process development and review some economic factors affecting the implementation of the new technology. Process analysis The new beet juice purification process was completely simulated in a pilot plant for several campaigns. Although altemative unit operations may be considered, the flow diagram in Figure 1 represents the major steps of the process. Because the raw beet juice is treated with ion-exchange resin in softening and chromatographic operations, removal of suspended solids becomes very important. Depending on the factory location and beet pretreatment the raw juice typically contains about % wt. suspended solids, about 30-50% is organic matter and the rest is silt and soil particles. Although some small pieces of beets are present in the diffusion juice, more than 50% of particulate matter is below 1-2 micron in size. It has been shown that even the submicron particles tend to accumulate in the resin beds creating problems with liquid distribution and pressure drop. The size of the suspended particles makes it very difficult to remove them using conventional filtration methods. In this particle size range crossflow filtration, such as micro- or ultrafiltration appear to be extremely efficient. 167

2 Depending on the type ofmembrane and module design juice pretreatment requirements may be more or less strict. For example, membranes with relatively large feed channels can tolerate larger amount of suspended solids and fibrous material, while additional screening may be required for narrow feed chmmels. The concentration of suspended solids affects the final quantities of concentrate sludge that will need to be dewatered and desugarized to make the process feasible. ARi has developed and verified on large pilot scale a pretreatment process capable ofeliminating 75-80% of suspended solids prior to membrane filtration. Although sugar technologists were among the first testing membranes for different applications, the membrane materials and module designs were not r eady to meet the challenges of the sugar industry. It had been demonstrated very early in the development phase that any membrane with pore size below 0.2 micron can produce permeate of excellent quality. The possibility of purity increase across membranes has been debated, but for the raw juice purification process absence of suspended solids in the permeate is the only critical issue. Because membrane replacement becomes an essential part of the operating cost, membrane integrity and durability need to be extensively tested. The cost of the raw juice pretreatment as well as handling and disposal of the concentrate effluent stream must be estimated. Typically the cost of such a test program is quite significant to be absorbed by a single sugar company. An international group of several sugar companies and ARi initiated a research program in order to determine the best membrane for raw juice application and subject this membrane to a continuous factory-like operation. For several years of testing the Membrane Study Group has acquired significant experience and knowledge in membrane technology and collaborated with membrane manufacturers on optimization of their products to meet the specifications of the sugar industry. In general, it has been shown that some membranes can withstand the conditions of beet sugar manufacturing. The rest of the unit operations involved, other than membrane filtration, are routinely used in the sugar industry and the comfort level of using these technologies is rather high. Process integration Integration of a new process into exlstmg plants requires a gradual approach. The implementation strategy will be different for plants that already have chromatographic installations and for those that do not. Since the same installation with minor changes and the same ion-exchange resin can be used for molasses and concentrated raw juice, the first logical step would be to install the chromatographic separator for molasses along with required evaporators. At the same time juice softening equipment should be operated, because the separation ability of chromatographic resin is impaired by presence of divalent cations. Installation ofjuice pretreatment and a membrane system will allow a switch from molasses to raw j llice separation during the campaign and elimination of the lime purification process. In the off-season period chromatographic separator may be used for processing molasses from the other plants. Another option would be to store some portion of the concentrated and softened raw juice and process it later through chromatography and the sugar end. The alternative operation modes may be considered, which provide the best match for a company's strategic plan. 168

3 FIGURE 1 Raw Juice Purification Process Flow Diagram Beeta Pulp Animal Feed Pre-Treatrne,nt & Membrane Deaugarlzed mud Filtration Concentrated raw Juice Rafflnate W hite sugar Mola.aea Animal feed It is interesting to observe the effect of the new purification process on sugar end operation. As it has been mentioned il l an earlier paper, because of the higher purity of feed material the sugar recycle is drastically reduced. The size of the high raw and low raw handling equipment is, therefore, minimized. With the relatively low color chromatographic extract and its purity approaching 98-99% two or three successive white boilings may be possible. Because of lower expected molasses purity, a conventional three-stage boiling scheme may be insufficient. Therefore, part of the low raw equipment may be used for the additional crystallization. Lower quantity of the high and low raw fillmass will result in longer crystallization times and some energy savings. 169

4 Economic analysis A complete economic evaluation taking into account existing equipment must be performed for each plant in order to estimate the benefits of the raw juice purification process. Evidently, membrane fil tration alone does not provide the benefi ts necessary to justify the purchase of a largescale system. We have attempted to analyze whether membrane technology can replace conventional liming and carbonation assuming that it is complemented by chromatographic purification and softening. We consider this to be a reasonable approach to obtain first estimates offeasibility of the new technology. Molasses chromatographic desugarization had already been proven to be feasible for the US sugar industry. Therefore, it is necessary to show that the use of membrane filtration in the beet end can provide savings sufficient to justify the capital expens. Obviously, the results of our membrane study should provide th cost estimates for the complete economic analysis. The following assumptions proved to be useful for our analysis. 1. The chromatographic separator can be easily converted from molasses feed to softened and filtered raw juice. 2. The chromatographic separator can be economically justified based on extraction benefits. 3. Thin juice softening and additional evaporation requirements are included in the separator justification. 4. Changes in the sugar end are not included in the analysis, since they are specific for each plant. 5. The maintenance and operating cost estimates for a membrane system are taken from a quote provided by an equipment manufacturer. The quote was based the experimental data provided by ARi and the Membrane StUdy Group. We have thoroughly studied which areas of the beet end will be affected by the installation of a membrane filtration system. The largest contributors are listed in the Table 1. The estimated annual changes in operating cost are reflected in Table 2. The membrane replacement will be the major contributor to the operating cost in the new "lime-free" purification process. The annual replacement cost depends on membrane selection. For our analysis we have used the annualized cost of ceramic membranes under the assumption of five years membrane life time. The replacement cost would be similar for polymeric membranes with a lifetime of one campaign. The overall operating cost of conventional beet end in a 7,000 tons/day slice rate factory for a 160 day campaign was estimated at $4,180,000. This number includes cost of materials, labor, power and maintenance. Similar calculations for a beet end including a membrane system showed an expected operating cost of $2,366,000. The number also includes the membrane replacement cost. The resulting savings would be $1,814,000 per year or $1.62 per ton of beets. Depending on the acceptable payback period these calculations allow one to estimate an acceptable cost range for the membrane system. 170

5 Table 1 Materials eliminated or added in the beet eod Eliminated Lime rock and spalls Kiln fuel (coke or natural gas) Screened coke Soda ash Filter cloth for thin juice fi lters Filter-aid Reduced Defoamers and flocculating agents Added Chemicals for membrane cleaning Lime for fl ume ph adjustment Table 2 Expected cbanges io operating expenses Expenses Percent reduction Cost of materials and chemicals 67 Maintenance and repair* 55 Power usage 20 Environmental cost related to lime kiln and lime ponds operation 100 Labor 22 Membrane replacement added cost * Maintenance cost for a membrane system was estimated at 2.5 % of total capital cost according to reconunendations of a system manufacturer. REFERENCES l. Kearney M.,V. Kochergin, e.a., U. S. Patent 5,466, Kearney M. The Amalgamated beet/cane juice chromatographic separator, Int 'f. Sugar Journal, 1996, v. 98, No. 1168B, pp Kearney M., D. Rearick, Raw jui ce chromatographic separator, Proc. of SPRI Workshop on Separation Processes in Sugar Industry, ed. M. Clarke, 1996, p ~-