Evaluation Performance of the Steam Power Plant in Iraq Based on Energy and Exergy Analysis

Even with the availability of energy sources and fossil fuels (oil), The electricity sector in Iraq suffers from shortage of electric power, especially in light of population expansion. So, should be many initiatives are being taken to improve and enhance fossil fuel-powered steam plants in order to boost their effectiveness and lower energy losses. The disparity between global energy production and demand is getting less every day. Energy consumption is a key indicator of both a country's and a community's degree of development and quality of life. The capacity augmentation is necessary to meet these energy demands for effective use of energy resources; thermal system analysis is crucial. The first law of thermodynamics or energy analysis is the conventional method for analyzing thermal power systems. Inaccurate data on efficiency and losses cannot be gleaned from energy calculations predicated on the first law of thermodynamics. Consequently, there is considerable attention on effectively combining the first and second laws of thermodynamics [1]. Ray et al. [2] locating the causes of high irreversibility across a power cycle's various parts is helpful information for exergy analysis. Loss of usable work is easily measurable over time and under various operational conditions. When the pace at which a component's exergy is destroyed increases and its exergy efficiency falls below its design value, it is in a state of progressive deterioration. Rosen and Scott [3] supposed, the term "energy" is frequently employed in studies, including the study of energy production, transformation, and consumption. However, these studies on exergy are often more informative than those on energy. Exergy-related losses provide a more precise identification and description of the magnitudes of thermodynamic losses as well as their origins, locations, and causes. The energy industry may be seen more clearly with the help of exergy. Exergy analysis is helpful because it highlights potential sources of inefficiency in energy systems during the design phase. Cengel et al. [4] presented that exergy is the highest amount of useful work that a system is capable of producing in a given environment and state. When it comes to the optimization of intricate thermodynamic systems, the exergy investigation, which is founded on the second law of thermodynamics, has shown to be an extremely effective tool that can determine the locations and sizes of the biggest irreversibilities in these cycles. Rosen [5] explained that exergy analysis recognizes that while energy cannot be generated or destroyed, it can decline in quality until it reaches a point where it is completely equilibrated with the environment and is therefore no longer useful for completing tasks. Dewulf et al. [6] elucidated that when a system or resource is brought into equilibrium with its surroundings through reversible processes and is solely permitted to interact with the environment, the exergy is the maximum amount of useful work that may be obtained from that system or resource. Proper consideration must be given to the environment employed in the calculations, such as the so-called dead state. Al-Mubaddel et al. [7] the condenser is an essential component of thermal power plants that utilize the condensation process, which entails the transformation of saturated steam exhaust from the LP turbine into liquid water. In addition, non-condensable dissolved gases are eliminated. Utilizing a condenser in a thermal power unit also improves the efficiency of the power plant by rejecting heat to the environment; hence, they have examined the effect of environmental factors on the condenser of the steam power station. Aljundi [8] have investigated the impact of changing the environment's temperature from 283.15 to 318.15 K on the degradation of exergy on major portions of Al-Hussein thermal power plant in Jordan by employed energy and exergy analyses. Ameri et al. [9] evaluated the effect environment condition on the exergy efficiency of the Hamedan steam power plant at different loads. the study had shown the efficiency decreased with increased ambient temperature. Altering the condition dead state had been studied for C¸ayırhan thermal power plant located in Turkey [10]. The second law efficiency of station decreased with increased ambient temperature at constant pressure. Studied the effect climate condition and condenser pressure of Shahid Montazeri power plant shows that the decrease the performance of the station due to rise in vacuum pressure of condenser [11]. The investigators [12] examined impact of altering condenser pressure of North Refineries Company (MRC)/ Baiji/ Iraq appeared that the second law efficiency was growing.

The objective of the presented paper is to perform a power and energy assessment on the 225 MW Al-Mosyab steam power plant's No. 3 unit to determine where energy is lost and how much exergy is destroyed in each section of the station. In addition, this paper studies the effect of changing cooling water temperature and condenser pressure on plant effectiveness. Thus contributing to improving the performance of steam stations operating in Iraq.

Thermodynamic model equations are used to evaluate the performance of various plant components and the entire plant. For each control volume, the model equations are essentially derived from the fundamental laws of mass conservation, energy conservation, and exergy balance. All model equations are solved with engineering equation solver (EES) [13] software based on the readings of unit-3 summarised in Table 1 which displays the operating conditions under which the 225 MW of power it produces. These equations are applied to various plant components based on the following assumptions: environment references are (298 K and 1bar), steady state control volume. The kinetic and potential of energy and exergy were not taken into account as ref. [14, 15].

Balance of mass, energy, and exergy are calculated as following:

$\sum \dot{m}_i=\sum \dot{m}_e$                          (1)

$\dot{Q}-\dot{W}=\sum \dot{m}_i h_i-\sum \dot{m}_e h_e$                           (2)

$\dot{X}_{\text {heat }}-\dot{W}+\sum \dot{m}_i x_i-\sum \dot{m}_e x_e=\dot{X}_{\text {des }}$                           (3)

where, $\dot{X}_{\text {heat }}$  is the rate of exergy transfer by heat can computed by:

$\dot{X}_{\text {heat }}=\sum\left(1-\frac{T_o}{T_k}\right) \dot{Q}_k$                           (4)

The specific exergy can get by:

$\dot{X}=\dot{m} x$                           (5)

The specific exergy can get by:

$x=\left(h-h_o\right)-T_o\left(s-s_o\right)$                           (6)

The net power has been calculated as [16]:

$\begin{aligned} & \dot{W}_{n e t}=\dot{W}_{u, H P T}+\dot{W}_{u, I P T}+\dot{W}_{u, L P T}-\dot{W}_{u, B F P} \\ & \text { - } \dot{W}_{u, C E P} \\ & \end{aligned}$                           (7)

The exergy content of fuel which represent the exergy supply to the system is written as:

$\dot{X}_{f u e l}=\dot{m}_{\text {fuel }} * \varphi * L H V$                           (8)

where, φ is ratio of chemical exergy of liquid fuel and LVH is lower heating value represent the amount of NCV of crude oil at Table 1.

Power plant second law efficiency and exergy destruction are calculated by:

$\eta_{\mathrm{II}}=\frac{\dot{W}_{\text {net }}}{\dot{X}_{\text {fuel }}}$                           (9)

$\dot{X}_{\text {des }}=\sum \dot{X}_{\text {des,compnent }}$                           (10)

Power plant Thermal efficiency is computed by Eq. (11):

$\eta_{t h}=\frac{\dot{W}_{n e t}}{\dot{Q}_{B L R}}$                           (11)

where, the $\dot{Q}_{B L R}$  can calculated by:

$\dot{Q}_{B L R}=\left(\dot{m}_{13} * h_{13}+\dot{m}_{18} * h_{18}+\dot{m}_{B D} * h_{B D}\right)-\left(\dot{m}_{12} * h_{12}+\dot{m}_{17} * h_{17}+\dot{m}_{R 1} * h_{R 1}\right)$                        (12)

The exergy study estimates that the plant can destroy 412 MW of exergy. Most of the exergy waste comes from the boiler, at 86.48%. 3.36%, 2.3%, and 2.41% of the total exergy destruction occurred in the HP turbine, IP turbine, and (LP) turbine, respectively.

According to a comparison of the performance of the turbines, it becomes clear that the IP turbine is the most efficient in terms of the second law of thermodynamics at 90.36 percent, whereas the HP turbine is the least efficient (at 79.91%).

Increasing condenser pressure led to worse thermal and second law efficiencies. In additional the net power output can be decreasing by 3.61% MW and increase in the exergy destructions of the cycle by 2% MW.

The cooling water temperature significantly impacts the performance of the generating unit. It increases the heat wasted from the condenser, also impacting the efficiency of the steam power plant and controlling the turbine's output. Clearly, when the temperature of the cooling water inlet rises, this causes the thermal efficiency and second law efficiency can degrade by 1.196%, and 1.203%, respectively and the net power can fall by 0.57%. The total energy wasted and exergy destruction of the power plant increased by 18.33 MW and 0.57 MW, respectively.