Historically, Egypt’s favourable conditions in the Nile valley and in the Nile delta have given the country a comparative advantage in a number of major food and fibre crops, particularly wheat, rice, maize, and cotton. After the harvest operation is finished, these crops produce huge amounts of residues (leaves, stalks, straw etc.). The total amount of these residues reaches about 16 million tons of dry matter per year. The average yields of the main crops and their residues in Egypt are presented in Figure 3.1. For example, the average yield of cotton stalks is about 4.5 t/ha per year. Cotton stalks represent about 9% of the farm residues in Egypt. About 90% of these residues can be used as energy resources (MALR, 2002).

Fig. 3.1: The average yield of the main crops and their residues in Egypt (MALR, 2002)

Previously, farmers stored these residues for domestic purposes. Following the environmental problem of burning cotton stalks, only a small amount is now used illegally by farmers' families for domestic purposes. Figure 3.2 shows the energetically usable and used main crop residues in Egypt. Long straw varieties of wheat are preferred because the straw is of high value (Carig, 1993). Straw is used as animal feed in the summer and for brick-making in the villages of some regions. Therefore it is not used for bioenergy purposes. Rice straw is used mainly for animal feed and bedding. A small amount is used in the paper industry. The annual amount of rice straw is about 3.6 million tons/year. Rice straw was burned on the field at the same time as cotton stalks too. It was also an important factor for the pollution problem. Therefore burning of rice straw on the field was also prevented by Law No. 4 for the year 1994 (EEAA, 1994). This law was applied in 1999, preventing the farmers from burning any crop residues on the fields. On the other hand, the energy equivalent of the energetically usable residues in Egypt reaches about 112 PJ/year (MALR, 2002). These residues can be used as environmentally friendly biofuel if they are well formed and handled.

Fig. 3.2: The energetically usable and used main crop residues in Egypt (MALR, 2002)

The use of farm residues for energy purposes requires a study of their physical and chemical properties. This involves analysing these residues and characterizing their differences in use as a fuel. The heating value (H) is one of the most important properties. The heating value describes the energy released upon combustion of a unit mass of fuel. It is an important thermal property for modelling conversion systems. The heating value is reported as higher (gross) heating value or lower (net) heating value. The values are related to the fuel elemental analysis and moisture content. As shown in Table 3.1, farm residues have a high heating value, particularly cotton stalks which have a higher value by comparison with the other residues. The elemental analysis supports this material as good quality for energetic purposes.

Table 3.1: Heating value and compositional data for solid biofules