WP4: Integration of CCL into a Full-scale Hard Coal Power Plant (UNP)

This work package studied the integration of the CCL technology into a full-scale coal-fired power plant. The existing Emile Huchet Unit 6 power plant, located in Saint-Avold in France, was selected to conduct the study. Owned and operated by Uniper, this is a 600 MWe coal-fired power station fitted with flue gas desulphurisation (FGD) and selective catalytic reduction (SCR) for reduction of SOx and NOx respectively.

Although the Emile Huchet power plant burns a variety of world-traded bituminous coals with varying sulphur content, for the purpose of this study it has been assumed that the plant combusts a single coal. The Emile Huchet power plant cases selected in the study are listed in Table 1. These represent the design (100 %), the minimum (52 %) and two intermediate 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 1: Load Cases and flue gas properties from power plant

Load % 100 81.0 66.3 52.0
Fuel input t/h 213.07 172.58 141.30 110.88
Thermal input MWth 1505.12 1238.31 1008.19 752.29
Gross power MWe 623.1 510.0 407.5 303.6
Auxiliary power MWe 35.2 30.2 26.6 23.5
Net power MWe 587.9 479.8 380.9 280.1
Net efficiency % 39.13 38.78 37.84 36.94
CO2 vol.% 10.18 9.54 8.33 7.21
H2O vol.% 11.40 11.40 11.40 11.40
SO2 ppmv 55.69 52.18 45.54 39.41
O2 vol.% 6.67 7.42 8.84 10.16
N2 vol.% 71.75 71.64 71.43 71.23
Mass flow kg/s 901 777 725 654

A simplified process scheme of the calcium carbonate looping process with the secondary water-steam cycle is shown in Figure 1. Within the calcium carbonate looping process, two hot gas streams at a high temperature level are used for steam generation: the CO2-depleted flue gas from the carbonator at 650 °C and the CO2-rich stream from the calciner at 900 °C. The heat that needs to be extracted from the carbonator is supplied to the secondary power cycle as the third heat source.

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. In this equation, ηref expresses the reference electric efficiency of the whole unit without CO2 capture, ηEH6 the electric efficiency of the power plant and ηsec,CCL the electric efficiency of the secondary water steam cycle attached to the CCL system. The last two efficiencies were weighted by the corresponding share of the thermal duty, QEH6 and QCCL.

  (1)

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 overall net electric efficiency and the efficiency penalties related to the weighted reference efficiency calculated using Eq. (1). The net efficiency penalty for the full-load case was approximately 3.5 percentage points without CO2 compression and 7.0 percentage points including the CO2 compression system. During minimum load operation, these numbers increase to 4.9 / 8.6 percentage points which is mainly due to the reduced CO2 concentration in the flue gas from the power plant.

Figure 2: Net Electric Efficiency and Efficiency Penalty at Different Power Plant Loads

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.

The most significant component of the direct cost for integration of a calcium looping process with a hard coal power plant for CO2 capture is the CCL capital cost. A bottom-up approach was used to estimate the overall unit cost for this study. To get the basic information about the system with CO2 capture, mass and energy balances (including utility calculations) were generated. A detailed cost model for the CCL plant including main equipment, design and installation was developed for the CCL CO2 capture integration. A breakdown of the capital cost is shown in Figure 3. For the selected 600 MW power plant, the CCL plant capital cost was estimated to be about €669 million, giving an additional specific investment of €724/kWe.

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

In this study, the amount of CO2 avoided was 771.9 g/kWh. The CO2 capture cost and CO2 avoidance cost relative to the corresponding reference plant were €15.4/t CO2 captured and €20.2/t CO2 avoided, respectively.

A comparison between CCS technologies was performed. The results showed that using the CCL technology in hard coal power plants for CO2 capture instead of MEA post-combustion or oxyfuel combustion technologies gave an improvement in the capture efficiency and the cost of CO2 avoidance.

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 hard coal power plant with and without CCL. The environmental impacts of the plant technology and its potential hazards to human, wildlife, and bio-systems were considered. The LCA was carried out using the ReCiPe methodology, and both the midpoint and endpoint were considered. SimaPro 8.3 was used to model the system. The study assumed that the 600 MW power plant was operating at full load. The study was a cradle-to-gate type, and capital goods were not included. The electricity retained 100 % of the environmental burden. This was because the CCL is a cleaning system. Its resultant product, CO2, has no value. 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 than without CCL. The damage assessment results indicate a 60 % and 68 % reduction in potential impact for the human health and ecosystems indicators respectively. This is achieved via a 9 % 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 increased use of resource will have an environmental impact. However, this has to be balanced against a 72 % reduction in the climate change impact category. Impact categories that were reduced by the retrofit of the CCL technology are those that are normally affected 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 hard coal power plant.  The increased resource use can 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 hard coal power plants