Why the emerging strong interest in vertical continuous pans?

SEVERAL OVERSEAS CANE sugar industries are implementing steam efficient practices in factory processing in order to achieve greater economic value from bagasse, e.g. from cogenerated export power, paper pulp, particle board and (maybe soon) second generation biofuels and chemicals. Many of these factories have installed falling film evaporators as part of the drive to steam efficiency. More recently, strong interest is developing in using vertical continuous vacuum pans (CVPs) with mechanical agitation to undertake evaporative crystallisation on low pressure vapour (e.g. using vapour 3 or vapour 4 bled from the evaporators). The cane sugar industry to now has mostly used horizontal CVPs as the horizontal layout provides several advantages over the vertical orientation. However, besides the suitability to readily incorporate mechanical agitation, vertical CVPs provide other benefits such as ease of bypassing a module for cleaning. This paper examines the advantages and disadvantages of the two continuous pan layouts. Aspects that are considered are the implications for steam efficiency, relative crystallisation rates, quality of the size distribution in the product massecuites and operator friendliness. A flowscheme is proposed for Australian factories to utilise horizontal and vertical CVPs for the production of A and B massecuites using vapour 3 (or vapour 4). The use of the SRI magma preparation system would provide for fully continuous operation of plant for the high grade massecuite production.