*3.1. Case Study 1—IGCC Power Plant with CaO Looping*

The case study is represented by the steam-gas cycle of gross power output of 392 MWe connected to the pre-combustion technology of the integrated gasification combined cycle (IGCC) with integration of the carbonate loop. IGCC uses the high pressure gasifier to produce pressurized gas (synthesis gas) from the carbon-based fuels [12]. The principle of the system is based on steam-gas cycle with hydrogen combustion and with integrated gasification of lignite with CO2 capture from the gas before combustion. The IGCC system ensures the removal of impurities such as sulfur dioxides and particulates from the syngas before the actual carbonate looping. The case study represents a specific technology, where the elimination of the acid impurities is based on high temperature desulphurization by adsorbent of CaO/CaCO3.

The main advantage of the calcium looping system is the high degree of CO2 removal (up to 95%) and the process of simultaneous desulfurization [20].

To understand and define the system's boundaries while comparing scenarios, it is important to describe both scenarios from technical point of view.

The IGCC process can be divided into the following technological segments (Figure 1):


#### 3.1.1. Fuel Management and Treatment

The management of the fuel comprises lignite mining, transportation, storage, crushing (max. 40 mm), drying and grinding (max. 200 μm). Lignite is expected to be mined from the CSA (Karvin ˇ á region) quarry due to specific parameters (low concentration of ash). The lignite is then transported by railways to the storage located next to the power unit, ground, and dried to 200 μm with a maximum level of moisture (11%). The process of lignite drying uses the energy from the steam produced in the steam-gas cycle. For drying we expect use WTA (waste heat utilization) technology.

#### 3.1.2. Oxygen Production

Oxygen will be produced in the separated oxygen unit. The recommended process of the oxygen separation from the air is the cryogenic separation, a well-known and viable process. The electricity used for the cryogenic separation will be generated from the steam–gas cycle. The main outputs from the cryogenic separation are oxygen with 95% purity and nitrogen with purity of 98.7%. The nitrogen is then mixed with hydrogen as a fuel to the steam–gas cycle.

*Energies* **2020**, *13*, 4188

**Figure 1.** System boundaries for Scenario 1 (marked red are energies returning back to the system; dashed lines with numbers represent technological segments).

#### 3.1.3. Gasification Process

The gasification process of lignite is operated in a Shell generator (considered a modern and verified technology for this process). This type of generator ensures the lowest content of organic compounds that can create problems in the further purification process. In the generator, the oxygen reacts with the lignite (chemical reactions (1) and (2) [21]) in an exothermic reaction, creating a temperature around 1500 ◦C. In this temperature, the ash from the fuel is transformed into liquid slag. Gas coming out of the generator is cooled down by the injection of water to the temperature of 900 ◦C.

$$\text{C} + \text{O}\_2 \rightarrow \text{CO}\_2 \text{ } \Delta H \text{=}-394 \text{ kJ/mol} \tag{1}$$

$$\text{C} + 0.5\text{ O}\_2 \rightarrow \text{CO } \Delta H = -111 \text{ kJ/mol} \tag{2}$$

3.1.4. High-Temperature Purification Process, Water Gas Shift Reaction, and Carbonate Looping

The high-temperature purification process includes high-temperature desulphurization at temperatures between 800–900 ◦C. Desulphurization is done via adsorption of all the acidic impurities (e.g., H2S) on sorbent CaO/CaCO3 (reaction (3)) [22] that comes from the carbonator. The waste product after the purification process is a mix of CaCO3 + CaSO4, which is transported as waste to a landfill.

$$\text{CaO} + \text{H}\_2\text{S} \to \text{CaS} + \text{H}\_2\text{O} \tag{3}$$

The output from the purification process is purified gas. The gas is then transported into the water–gas shift reactors where the shift reaction is achieved. Said reaction (4) [21] converts CO into CO2 by steam. The purified gas after the shift reaction contains a higher rate of CO2.

$$\text{HCO} + \text{H}\_2\text{O} \rightarrow \text{CO}\_2 + \text{H}\_2 \text{ } \Delta H = -41 \text{ kJ/mol} \tag{4}$$

After the shift reaction, the gas is transported into the carbonate loop system, where the CO2 is separated. At first, the gas enters the carbonator. In the carbonator the exothermic reaction of CaO with CO2 takes place (reaction (5)) [21].

$$\text{CaO (s)} + \text{CO}\_2 \text{ (g)} \rightarrow \text{CaCO}\_3 \text{ (s)} \,\Delta H = -178.2 \text{ kJ/mol} \tag{5}$$

The temperature in the carbonator should not exceed 800 ◦C. The gas after the carbonation process proceeds into the combustion chamber with turbine.

The produced CaCO3 from the carbonator is transported into the calcinator that works in the oxyfuel regime. The temperature in the calcinator increases to 950 ◦C and the CaCO3 is decomposed back into CaO and CO2 (reaction (6)) [21]. CaO returns into the carbonator to be used as sorbent. Moreover, a fresh batch (2.5 t/h) of CaCO3 is periodically (once in 20 min) added into the calcinator.

$$\text{CaCO}\_3\text{ (s)} \rightarrow \text{CaO(s)} + \text{CO}\_2\text{ (g)}\ \Delta H = -178.2 \text{ kJ/mol} \tag{6}$$

The emissions from the calcination process (mainly CO2) are cooled and compressed. The liquefied CO2 is separated. The CO2 compression requires auxiliary energy, provided from the steam–gas cycle.
