Cement Energy & Environment

44 Exergy mapping enables engineers to identify where energy recovery offers the highest return. For instance, optimizing secondary air recovery and minimizing false air ingress can reduce fuel use by 1–1.5%. When combined with MPC, total system efficiency can improve by 5–6%. 4. COOLER OPERATION AND WASTE-HEAT RECOVERY Efficient cooling not only ensures high clinker reactivity but also enables heat recovery for combustion air. Poor air distribution can create “red rivers” or “snowmen,” leading to uneven cooling and energy losses. Modern grate coolers with variable-speed drives and optimized air chambers have greatly improved stability. In Plant 4, 3D laser scanning was used to map clinker bed profiles in real time. This data allowed automated adjustment of grate speed and air distribution, achieving uniform cooling at 55°C/ min. The secondary air temperature increased by 70°C, improving combustion efficiency. Table 2 – WHR Performance Examples Plant WHR Technology Power (kWh/t cl) Exhaust Temp (°C) Plant 4 (India) ORC + TEG 16 180 Plant 5 (India) ORC 15 250 Plant 6 (India) Climeon ORC 14 180 Table 3 – Alternative Fuel Properties Fuel LHV (MJ/kg) Ash (%) TSR Limit (%) CO 2 Saving (%) Operational Note RDF 16 12 80 15 Quality variation Biomass 14 6 60 12 High moisture Tyres 28 5 20 5 High Fe content H 2 120 0 20 100 Storage issues NH 3 18 0 30 100 NOx control needed India’s WHR capacity has now exceeded 130 MW. Typical yields are 14–16 kWh/t clinker depending on exhaust conditions. Waste-heat recovery units—especially Organic Rankine Cycle (ORC) and Thermoelectric Generator (TEG) systems— convert low-grade heat (150–300°C) into power. Combined with AI-based process optimization, WHR contributes to both emission reduction and energy independence. 5. ALTERNATIVE FUELS AND COMBUSTION STABILITY Replacing fossil fuels with alternative fuels (AF) such as RDF, biomass, and rubber waste is now central to sustainable operations. As shown in Figure 2, CO 2 emissions decrease rapidly with increasing TSR (Thermal Substitution Rate) up to about 85%, beyond which the benefits plateau. Figure 2: TSR vs Specific CO2 Combustion Suitability (Blue line shows CO 2 falling sharply up to ≈85 % TSR, then flattening.) In Plant 5, TSR reached 75% using RDF and biomass blends, resulting in a 13% CO 2 reduction and an 18% drop in fuel cost. Flame imaging and oxygen sensors were used to stabilize the burning zone despite varying fuel properties. Specific CC CO 2 Emission TSR (%) Figure 2 - TSR vs Specific CO 2 Emisiion 0 40 60 80 100 900 850 800 750 700 650 0