ENGINEERING AND ENERGY WORKSHOP ON FACTORY DESIGN
Florenal Zarpelon Chairman, Engineering & Energy Section
The ISSCT Workshop on Factory Design, organized by Shakarganj Sugar Research Institute at Faisalabad, Pakistan, from Feb. 23 to 28 1997, was a success. There was a total of 52 participants,among them 26 foreign.
The first two days delegates visited Shakarganj Sugar mill and distillery, Crescent Sugar Mill and particle board plant, Fauji Sugar Mill, and Shakarganj Research Institute.
Concerning the Workshop itself, there were very good contributions for all the themes reviewed. The technical session was opened with the topic Milling versus Diffusion which was covered by Dr. Peter Rein from South Africa. The advantages of the diffusion technology were emphasized and comparison between milling and diffusion covered the following aspects: in milling it is very difficult to obtain 97% extraction while 98% is normal with diffusion; power requirement for cane preparation is more or less the same for both but for extraction it is 50% less with diffusion and thus, there is an opportunity to export more energy; in a 300 tch mill an extra 2 MW can be obtained with diffusion. For a high extraction unit, the cost ratio between diffusion and milling can be figured out as follows: capital cost is of the order of 60%, total maintenance cost 57% and operation labour cost under average conditions is 50%. Juice heating is fundamental for diffusion in order to eliminate microorganisms and to promote rate of extraction; for this reason there is a slight overall increase in the process steam demand for diffusion. With regard to juice quality, it was pointed out that diffusion gives a lower starch and suspended solids content, with reduced purity and about 25% more colour. Diffusion is more sensitive to trash and gives around 6% more bagasse since all bagacillo is retained in the extraction unit. Filter cake produced under diffusion is around half. Lactic acid is much less in diffusion which means less microbiological activity. The issue of bagasse moisture was raised and it was mentioned that in Hawaii bagasse moisture from diffuser is of the same order as that from milling and whether milling or diffusion is practised, bagasse dewatering is governed by fine grooving, 400 pitch angles, adoption of messchaert grooves, hard facing, drain of the bagasse before getting to the mill and speed of the mill as low as possible to prevent reabsorption. Another important issue was in regard to change from milling to diffusion: the expansion of the capacity of the factory is a good opportunity for that purpose.
Sugar quality trends and sugar boiling design were covered by Dr. Ross Broadfoot, from Australia. A revision was made on the characteristics of mill white, refined and high quality raw sugar and sugar quality criteria based on colour, polarization, ash, suspended solids, moisture, dextran, starch, size distribution and temperature. A review of the process now being used in white end refinery attached to a raw factory, a stand-alone refinery and a direct mill white using floatation technology. An introduction to emerging membrane technologies was also presented, including New Applexion Process (ultrafiltration / juice softening) and Honiron ABC process (continuous screening, ultraclarification and absorption), and a review of recrystalization processes was given. Sugar boiling procedures used in different countries were presented to show the various options of the technology. Continuous boiling was covered by Dr. Rein; he emphasized that the problems related to encrustation are only encountered with high grade pans.
Power generation at high demand of process steam was presented by Florenal Zarpelon, from Brazil. A modern sugar factory is nowadays an energy complex where alcohol and other by-products are also produced. Under these circumstances maximization of power generation is a question of the optimazation of the energy (energy conservation or first thermodynamic law) and the optimization of the combination steam production and steam turbine, as stated by the second thermodynamic law. The process of mechanical vapour recompression (MVR) was discussed and the conclusion is that MVR is applicable to reduce fuel consumption under high demand of process steam; it is not effective to improve power generation. Boris Morgenroth, from Germany, presented the results obtained using the Balcke-Durr falling film plate evaporator in South Africa. Robert Kwok, from Hawaii, gave an overview of the bagasse gasification demonstration plant installed at Paia mill.
Sugar drying and conditioning was covered by Dave Meadows, from South Africa. He presented the main types of sugar dryers used in the sugar industry and the problems related to sugar storage.
On the theme “Green cane factory impacts”, a very interesting presentation was made by Robert Kwok on “Effect of green cane harvesting on factory operations in Hawaii”. He mentioned the strong environmental resistance to cane burning in Hawaii since the island economy is heavily dependent on the tourist industry. The operation with green cane results in a number of problems, among them were mentioned: lower washing efficiency of the cane, problems of cane preparation, low milling rate, reduced mill extraction, mill slippage, high ash in bagasse, poor burning of bagasse, poor clarification, high juice colour, low crystallization rate, high viscosity, poor sugar quality. The “impacts of extraneous matter on sugar factory recovery” was presented by Muhammad Qureshi, from Pakistan, who discussed the high losses in Shakarganj Mills due to cane trash.
Trends on steam Generation were presented by George O Reilly, from South Africa. He made a real contribution since he replaced John Briggs of Foster Wheeler, Canada, who could not come to the Workshop. George discussed general aspects of boiler design, emphasizing grate design, gas cleaning, ash disposal, rate of steam production, air heater and economiser.
Dr. J. Bhagat, from India, covered the topic “Economics of small mills”. A good discussion was undertaken on this subject, and the conclusion was that it is difficult to establish a comparison among countries since different conditions are present.
Philip Steiner, from South Africa, gave an overview on “Minimum staffing, automation and control”. It was shown that automation provides real information to make a decision for optimum plant performance. The Komati Mill in South Africa, with its centralised control room, intelligent devices and distributed controls systems, was mentioned as an example of a modern automated sugar mill.
Other general topics were covered by Dr. Mohammad Munir, from Germany (Sugar graining techniques), Abdul Q.Khattak, from Pakistan (Factories handling beet and cane simultaneously), Peter Jais, from Brazil (High throughput of Brazilian mills).