244 M.J. Lewis Table 9.1. Summary of mechanical solid separation techniques Solids from liquids Principles: gravity, centrifugal, electrostatic, magnetic centrifugation Examples: gravity settlers, centrifugal clarifiers, hydrocyclones; use of chemical floc Filtration:(see also Chapter 8; fat fractionation) Principles: gravity, vacuum, pressure and centrifugal Examples: sand and cake filters, rotary vacuum filters, cartridge and plate and frame filters, microfilters( Chapter 5): use of filter aids Solids from gases Principles: sedimentation and filtration Examples: cyclones, bag filters, electrostatic precipitators 200 mg m-to below 10 mg m air. The powder can be recovered from the bags and the clean air'can be used for heat exchange. Further details are provided by Knipschildt (1986) However, rather than removing all the particles, there may be a requirement to fractionate the powder, based on particle size(see Sections 9.3 and 9.4). This example illustrates the theme for this chapter, where the main emphasis is placed on the separation of components from within a solid matrix. Solids come in many forms, shapes and sizes, so the first part of the chapter will be devoted to discussion of the main properties of solid foods which will influence the different types of separation processes 9.2 PHYSICAL PROPERTIES OF SOLIDS Solids come in a wide variety of shapes and sizes. All solid foods are particulate in nature and there are a wide range of sizes and shapes to contend with. Some examples are illustrated from the different food sectors in Table 9. 2. It should be noted that although all these foods are regarded as solids, their moisture content may range from less than 10% to greater than 90%. Their moisture content and chemical composition can be found from foods composition tables, for example Paul and Southgate (1978)(see also Chapter 2 Indeed, one of the main objectives is often to remove selected components from the food Some operations where separations from solids is involved and constitutes an impor- tant part of the process are cleaning of agricultural produce(see Section 9.6.3); sorting and size grading, particularly for quality grading of fruit and vegetables peeling of vegetables, dehulling of cereals and legumes and deboning or shelling of meat and fish fractionation or recovery of the main components within the foods, e.g. proteins, fat, carbohydrates and minerals244 M. J. Lewis Table 9.1. Summary of mechanical solid separation techniques Solids from liquids Sedimentation: Principles: gravity, centrifugal, electrostatic, magnetic centrifugation Examples: gravity settlers, centrifugal clarifiers, hydrocyclones; use of chemical floc￾Filtration: (see also Chapter 8; fat fractionation) Principles: gravity, vacuum, pressure and centrifugal Examples: sand and cake filters, rotary vacuum filters, cartridge and plate and frame filters, microfilters (Chapter 5); use of filter aids culants or air flotation Solids from gases Principles: sedimentation and filtration Examples: cyclones, bag filters, electrostatic precipitators 200 mg m-3 to below 10 mg m-3 air. The powder can be recovered from the bags and the ‘clean air’ can be used for heat exchange. Further details are provided by Knipschildt (1986). However, rather than removing all the particles, there may be a requirement to fractionate the powder, based on particle size (see Sections 9.3 and 9.4). This example illustrates the theme for this chapter, where the main emphasis is placed on the separation of components from within a solid matrix. Solids come in many forms, shapes and sizes, so the first part of the chapter will be devoted to discussion of the main properties of solid foods which will influence the different types of separation processes. 9.2 PHYSICAL PROPERTIES OF SOLIDS Solids come in a wide variety of shapes and sizes. All solid foods are particulate in nature and there are a wide range of sizes and shapes to contend with. Some examples are illustrated from the different food sectors in Table 9.2. It should be noted that although all these foods are regarded as solids, their moisture content may range from less than 10% to greater than 90%. Their moisture content and chemical composition can be found from foods composition tables, for example Paul and Southgate (1978) (see also Chapter 2). Indeed, one of the main objectives is often to remove selected components from the food. Some operations where separations from solids is involved and constitutes an impor￾tant part of the process are: cleaning of agricultural produce (see Section 9.6.3); sorting and size grading, particularly for quality grading of fruit and vegetables; peeling of vegetables, dehulling of cereals and legumes and deboning or shelling of meat and fish; fractionation or recovery of the main components within the foods, e.g. proteins, fat, carbohydrates and minerals