**2. Description of process flow diagram**

Quarrying is the first step of the cement manufacturing (see **Figure 1**). Inside the quarry that is close to the cement factory, low- and high-grade marl and limestone are mined by blasting. Further, the raw material with granulation of up to 800 mm has to be transported via dump trucks to the hammer crusher, where it is crushed to the granulation of 0–80 mm for marl and 0–50 mm for limestone.

The low-grade and high-grade marl and quartz (silica corrective material) are then stored separately. From the depository the raw materials are transferred to the vertical roller mill

**Figure 1.** Principal flowsheet of the cement manufacturing process.

with a capacity of 170 t/h and appropriate raw meal is produced. The storage of current raw meal has two silos with a capacity of 2200 t each.

The main goal of this chapter is to identify the potential of feasible energy recovery and to suggest pathways for a new concept design of heat exchange system avoiding the process traps and limitations. The maximum heat recovery of the particular cement manufacturing was obtained, and the updated heat exchange system was proposed. The author concluded that the energy consumption of the particular cement plant may be lowered by 30%. Thus, the features of the cement production process forced a methodology update to suggest feasible retrofit pathways with the objective of achieving the optimal temperature approach of the heat exchange system. There are different streams and processes that contain solid particles, gaseous phase and fast cooling down; these facts make a solution more complicated by the special construction of the process equipment, which causes impossible a heat transfer

Quarrying is the first step of the cement manufacturing (see **Figure 1**). Inside the quarry that is close to the cement factory, low- and high-grade marl and limestone are mined by blasting. Further, the raw material with granulation of up to 800 mm has to be transported via dump trucks to the hammer crusher, where it is crushed to the granulation of 0–80 mm for marl and

The low-grade and high-grade marl and quartz (silica corrective material) are then stored separately. From the depository the raw materials are transferred to the vertical roller mill

between some process streams.

96 Cement Based Materials

0–50 mm for limestone.

**2. Description of process flow diagram**

**Figure 1.** Principal flowsheet of the cement manufacturing process.

The prepared raw meal from the silos is supplied to the kiln. The kiln has an operation capacity of 90 t/h and upper bound of 110 t/h. A total of 57 t/h of the clinker is produced inside the kiln. For the heating of the raw mill, kiln raw meal, and a coal mill, hot flue gases from the kiln are deployed. Gases exit from a preheating tower with a temperature at about 370°C. Flue gases have be cooled down at the cooling tower because the filter bags cannot operate at the temperature higher than 140°C. The flue gases at the cooling tower are cooled to a temperature of 175°C by 10.5 m3 of cooling water. To further reduce the flue gas temperature from 175 to 105°C, fans are used to pump the ambient air. Flue gases go to the stack after filtration, and further, they are discharged into the environment.

At the kiln outlet side the temperature of the clinker is approximately 1450°C. At this stage, to preserve the clinker mineral structure, that is, its quality, the clinker has to be cooled very quickly to a temperature of approximately 150°C. A large amount of ambient air is introduced through seven clinker cooler fans to achieve the target temperature outlet. The ambient air is heated up to 290°C. After that, a small amount of this air is employed as an additional oxygen source in the kiln and a bigger part is supplied for cement mill heating if it is under operation. The operation mode with disabled cement mill envisages air cooling down before the filter bags. The gas has to be cooled to 105°C prior to the clinker cooler filter bags, after the gas is eliminated to the stack by four rows of four blowers.

The hot gases are needed for the cement grinding process. The hot air is taken to the separator where materials (clinker, limestone/slag and gypsum), pre-grinded on the roller press, are heated to extract moisture and prepare the resulting material for filter bags. They can be delivered from the clinker cooler or, in the case when the kiln does not operate, generated by a hot gas generator (HGG) with use of light oil as a fuel. It is the expensive option but it is used only in several weeks when the kiln overhauls. The consumption of the light oil is about 200 l/h.

A material mixture is kept in a bin with a capacity of 70 t that is supplied by a cement ball mill. Dust and fly ash are supplemented after the ball mill depending on the required kind of cement. The cement is then transferred through a bucket elevator to the next separator. Particles comprise the final product that is supplied to the cement silo.
