Cement, Energy and Environment

6 Results The thermal 7000 , - ---------------------, 6000 * @15%conversion efficiency, increased energy consumption due to recirculation already compensated 12 000 t/d 5000 -r-------------------~ power of the different systems used in the calculations with and without recirculation is summarized in Table 1. The thermal output varies between 7.6 and 45.1 * c: 0 9000 t/d MWth· assuming When a conversion efficiency of about 15 %, the generated electrical power ranges from 1 to about 6 MW (Fig. 4 ). A recirculation ·- - t1l ... g) c: g) CD ... g) ~ c. t1l u ... - u g) w 4000 -r----------------~ 6000 t/d 3000 +------ ----------'! 2000 3000 t/d 1000 0 system requires more fan power for compensating power demands of booster fans, pressure drop at the heat exchanger and cyclones and Fig. 4 Electrical power generation for different plant sizes similar aspects. These factors have been considered in our calculation of the electrical power generated, i.e. the additional energy consumption due to recirculation has been already subtracted from the energy produced by the system (see Fig . 4). The variation in the annual savings based on an electricity price of 0.07 US$/kWh is shown in Figure 5. For a 6000 Ud plant, the annual savings can easily reach about 1.5 million US$. When assuming specific costs for the supply and 3500000 ~----------------------- erection of a ORC– based WHRS of 2500 US$/kWh, this would • @0.07 US$/kWh 12 000 t/d 3000000 - .,.. "' 2. 2500000 +-------------------- • "' "" c: 9000 t/d "> 2000000 t---------------------------------. ~ 6000 t/d > .t: v ... w 1500000 +-------------------~ 4l -a; "' :::> ~ 1000000 <( 500000 0 3000 t/d Fig. 5 Annual electricity savings lead to a payback time of about 5 years. It IS clear that this calculation largely depends on the electrici ty price and on the specific costs for the WHRS. Thus the data needs to be evaluated for each plant individually. Any casU benefit calculation will benefit from public funding or national action plans for energy efficiency and environmental compliance. 14 I