Cement, Energy and Environment

2 Standard configuration vs. recirculation Power production and consumption figures have been calculated for plants having a 3000, 6000, 9000 and 12 000 tid capacity. In a ~tandard cement pyro line, common em1ss1on points are located at the main stack behind the preheater and at the clinker cooler vent air stack (Fig . 2). Only a portion of the cooling air necessary for the cooling of clinker has to be directed to a stack. A significant amount is already redirected to the kiln as secondary/tertiary air, providing a certain recuperation of thermal energy. Typical values of recuperated air range between 0.7 and 0.9 Nm 3 /kgcli· In order to reduce the number of variables in the calculations, a recuperation of 0.8 Nm/kgcli has been assumed in our calculations. In contrast, within the design of a recirculation system, cooling air is routed back to the clinker cooler circuit (Fig. 3). This principle has been known for several years, but now technology and materials have evolved, ensuring reliable operation and bringing -c 0 0 ... .r: "' c .r: - "' .Y. w ... 0 u.. .., significant benefits. A typical recirculation solution consists of the following components: • Cooler suitable for recirculation • Fans for elevated temperatures and moderate dust contents • Dedusting ·un it (cyclone or hot air filter) • Waste heat recovery system or heat exchanger • Booster fan(s) • Safety heat exchanger for upset conditions 3 Power generation with ORC About 35 % of the total input heat of a kiln line can be used for drying or power generation. Ki ln exhaust temperatures vary between 290-390°C, for the cooler between 250-350°C. Adapted ... ... "' '- "' -c C1l .r: E .r: "' Vl w w ... 0 ... u.. .., u.. 1.2 Nm 3 / kg, 1 to stack L Filter - · 'vV:;;f Only for upset condit ions 1 Vent a1r ~ c <l! > ... 0 ·- ... "' Total 2.00 Nm 3 /klc~o T=20 ·c Fig. 2 Standard scenario for clinker cooling Fi lter - 'vW! Only for upset condo! ions ~ t.= LL. "' Fig. 3 Cooler with recirculation Total 2.27 Nm 3 /kl," T=78 ·c designs lead to even higher temperatures, when mid-air is extracted. Power generation with ORC systems offers a number of benefits compared with common Steam Rankine Cycle Systems. One major advantage is the compact size of an ORC plant. Yet another benefit is that ORC plants can be automatically operated , whilst Steam Rankine Systems often need to be operated by specially educated (power plant) personnel. ORC systems show a high efficiency at partial load whi le the efficiency of steam-based systems drops significantly when operated below the optimum operating point. Start-up and shut-down procedures for ORC systems are fast and simple, while steam based systems need complicated and long lasting procedures. Finally, steam-based systems need significantly higher thermal input (temperature and mass flow) compared to ORC plants. 12 I I ~~ f ' l