WP5: Integration of CCL into a Full-scale Lignite Power Plant (RWE)

This work package studied the integration of the CCL technology into a full-scale lignite-fired power plant. The existing BoA1 power plant, located in Niederaußem in Germay, was selected to conduct the study. Owned and operated by RWE, this is a  944 MWe lignite-fired power station equipped with once through supercritical steam generators with single reheat and all necessary flue gas cleaning equipment for dust (electrostatic precipitator) and SOx (wet limestone FGD).

The BoA1 power plant burns a variety of Rhenish lignite from various local opencast pits. For the purpose of this work package, it has been assumed that the plant combusts a single coal for the power plant and the same pre-dried lignite in the CCL process. The properties of the coal are shown in Table 1. It has been assumed that this fuel will be used by both the power plant and the CO2 capture plant.

Table 1: Coal Properties

    as received pre-dried
Moisture % 54.5 12
Ash % 4.9 9.5
Carbon % 27.3 52.8
Hydrogen % 2 3.9
Nitrogen % 0.4 0.8
Oxygen % 10.3 19.9
Sulphur % 0.6 1.1
Gross calorific value MJ/kg 10.8
Net calorific value MJ/kg 9.01 19.7
CO2 emission g/kWh LHV 400

The BoA power plant cases selected in the study are listed in Table 2. These represent the design (100 %) and the minimum (48 %) loads. The load refers to the amount of fuel entering the burners divided by the amount of fuel required for the design value. A combustion calculation with the selected coal was conducted in order to make the study comparable with the assessment of other CO2-capture technologies. The composition and mass flow of the flue gas streams were calculated based on the power plant characteristics, mainly the excess air during combustion, the amount of leakage air, as well as the operation conditions of the FGD unit. Considering the conditions of the four different load cases, the composition of the flue gas streams was determined. Part-load operation of the host plant leads to considerable lower CO2 concentration in the flue gas. As the main consequence, the conditions for CO2 absorption in the carbonator worsen.

Table 2: Load cases and flue gas properties from lignite power plant

parameter unit load case
100% 48%
thermal input MWth 2195 1047
gross power output MWe 989 439
auxiliary power consumption MWe 45 31
net power output MWe 944 408
electric efficiency (net) % 43 39
electric efficiency (gross) % 45 42
CO2 vol.% 12.52 11.35
H2O vol.% 16.16 16.16
SO2 vol.% 0.01 0.01
O2 vol.% 4.19 5.45
N2 vol.% 67.12 67.04
mass flow kg/s 1118 589

A simplified process scheme of the calcium carbonate looping process with the secondary water-steam cycle is shown in Figure 1, as already shown in WP4.

Figure 1: Simplified Integration of CCL Process with Secondary Water Steam Cycle

To evaluate the efficiency penalties in comparison to the reference process without CO2 capture, an electric efficiency according to Eq. (1). was calculated. Based on the flue gas composition and mass flow, the CO2 absorption rate and subsequently the performance of the CCL whole system were calculated. The main results are shown in Figure 2. This figure depicts the net electric efficiency ηnet,CCL and ηnet,CCL+compr. as well as the arising net electric efficiency penalties Δηloss,CCL and Δηloss,CCL+compr. for the system without and with the COcompression. The net electric efficiency of the BoA1 unit at full load operation without CO2 capture is marked with the dotted red line. In the base case (pre-dried lignite) the net electric efficiency of the power system is 40.08 %, and 36.59 % considering the electrical demand of the CO2 compression unit. The efficiency penalties increase from 2.93 / 6.42 %points (pre-dried) to 3.59 / 7.37 %points (as received) for the system without and with the CO2 compression system, respectively, which is mainly due to the reduced CO2 concentration in the flue gas from the power plant.

Figure 2: Net electric efficiency and efficiency penalties for full and part load operation
as well as varying moisture content of the lignite

This study also estimated the capital investment and the operational and maintenance costs for the CCL unit in order to calculate levelised cost of electricity (LCOE) and CO2 avoidance cost using ECLIPSE software. The CCL technology has also been compared with other CO2 capture solutions.

According to the cost estimation approach in WP4, a breakdown of the capital cost is shown in Figure 3. For the selected 1000 MW lignite power plant, the CCL plant capital cost was estimated to be about €1022 million, giving an additional specific investment of €466/kWe.

Figure 3: Breakdown of the Capital Costs for the Calcium Looping Process

In this study, the amount of CO2 avoided was 685.7 g/kWh. The CO2 capture cost and CO2 avoidance cost relative to the corresponding reference plant were €19.8/t CO2 captured and €26.9/t CO2 avoided, respectively.

A life cycle analysis (LCA) was completed to evaluate the environmental impact of CCL technology integrated with the coal-fired power plant. The study made a comparison between the lignite power plant with and without CCL, according to the methodology presented in WP4. The endpoint damage assessment results are shown in Figure 4.

Figure 4: Endpoint Damage Assessment Results

The endpoint analysis indicates that generating electricity has a lower environmental impact with the employment of CCL as a decarbonisation tool then without CCL. The damage assessment results indicate a 52% and 80% reduction in potential impact for the human health and ecosystems indicators respectively. This is achieved via a 27% increase in the resource indicator.

The midpoint analysis indicates that some impact categories are lowered by the integration of CCL and others are raised. This is to be expected as the CCL plant consumes resources to function. An increase use of resource will have an environmental impact. However, this has to be balanced against an 82% reduction in the climate change impact category. Impact categories that were reduced by the retrofit of the CCL technology are those that are normally effected by the flue gas emissions; climate change, terrestrial acidification, particulate matter formation and natural land transformation.

Overall, the results indicate that the power plant with CCL has a lower environmental burden than the base lignite power plant. The increase resource use be justified by the reduction in the climate change impact.

This study could be expanded by including any potential CO2 credit resulting from the spent sorbent landfill capture, as well as any potential reduction from the cement plant calciner displacement. To complete the cradle to gate analysis the construction phase of the systems should also be considered.

Conclusion

The evaluation of economics and thermodynamics and the comparison to other CCS technologies show the advantages of CCL. The efficiency penalty and the CO2 avoidance costs are significantly lower compared to other technologies, i.e. amine scrubbing or oxy-fuel (see Figure 5).

Figure 5: Comparison of efficiency penalty and CO2 avoidance costs for lignite power plants