**6.3 Power generation integrated with brackish water desalination**

This concept applies to both simple Rankine cycle and combined cycle power plants. Instead of condensing the steam turbine exhaust against a cooling utility, the steam is exhausted at a back-pressure of about 15–25 psig, which is then used to drive a multiple-effect evaporator (MEE) desalination plant, increasing the overall site energy efficiency to about 75–80%. The MEE makes potable water from seawater or municipal and industrial wastewater treatment facilities effluent, thereby augmenting increasingly scarce freshwater sources. This is the direction KSA has taken.

To facilitate this transition, the formerly independent Ministries of Electricity and Water were merged at the direction of then King Abdullah. To the knowledge of the author, no other country in the world has taken such an enlightened policy initiative to promote national energy efficiency while simultaneously conserving the planet's precious limited freshwater resources. It can serve as a model for the rest of the world.

The energy efficiency initiatives undertaken in the Kingdom's Utility sector are estimated to improve the overall 2012 efficiency of 31.5% is to reach 45% by 2030 [8] as illustrated in **Figures 23** and **24**.

Concurrently, the power, fuel, and water utility supplies must be increased, and distribution infrastructure expanded to accommodate the rapidly growing population of the Kingdom.

## **6.4. Applications in utilities and power plant**

Saudi Aramco plays a critical role in supporting the Kingdom's evolving energy infrastructure. The overall average thermal efficiency of Aramco's interconnected on-site power generation facilities (CHP and CC as well) is 71.9%, while the national power grid efficiency in 2018 was around 38.7%. The savings from the

**Figure 23.** *Utilities map: 2012.*

*Energy Efficiency: The Overlooked Energy Resource DOI: http://dx.doi.org/10.5772/intechopen.101835*

#### **Figure 24.** *Utilities map: 2020.*

corporate energy program have reduced our CO2 emissions footprint since 2001 by about 50% per unit of production compared to "Business as Usual" prior to the year 2000. No other company worldwide has been able to match this documented metric to our knowledge. It gives the lie to companies that claim energy efficiency is not economically viable in order to conceal their hidden agendas.

The optimal energy strategy from the Kingdom's perspective would be for Aramco to operate its process-integrated cogeneration plants at full capacity, and to export any surplus power into the national electricity grid, to minimize fuel burning for electricity generation. As a result of the high thermal efficiency in 2018, Saudi Aramco saved approximately 263.8 MMSCFD of natural gas, compared to the average national energy efficiency. To improve power plant efficiencies, some best practices are as follow:

#### *6.4.1 GT compressor inlet air cooling*

The lower the inlet air temperature to the compressor of a GT, the higher the capacity as well as the energy efficiency. The air can be cooled in two ways by injection and evaporation of de-ionized water if the air is dry \*(as in arid regions), or by indirect cooling using absorption chillers driven by low-grade heat from the process, or by LP steam. The overall efficiency of the GT increases 10–15% from capacity gain. Both systems have their pros and cons.

The direct injection approach, also known as a "fogging system" is simple and cheap, and became very popular worldwide. Aramco jumped on the bandwagon too. However, it was soon noticed that our facilities began to report erosion of the initial efficiency gains over time. A long-term 4-year study of their efficacy conducted with the help of SRI international (San Antonio, USA) found that dissolved salts and fine particulate deposits on the compressor blades were the cause. On balance, the fogging systems did not deliver a net benefit, at least in Aramco GT installations.

Absorption chiller cooling technology offers the advantage of not introducing water which tends to favor adhesion of solids to the compressor blades. However, it is much more capital intensive and incurs higher maintenance costs.

The verdict on these options seems theoretically attractive, is neutral when practical contemplations are considered.

#### *6.4.2 Maximizing cogeneration units operation for power plants*

Provided the high incentive for exporting power from a facility, it's always recommended to maximize the operation of cogeneration units. The overall efficiency improvement from a combined cycle with a cogeneration unit vs. a simple Rankine cycle is about 30–35%.

#### *6.4.3 Conversion of simple cycle to combined cycle power plant with cogeneration*

Energy efficiency in a simple cycle power plant is in the range of 30–35% and that in a combined cycle power plant is 50–55%, and a combined cycle with cogeneration option can go up to 75–80%. So, it is strongly recommended that the system moves from a simple cycle to a combined cycle with the cogeneration option.

#### *6.4.4 Steam and water conservation by using steam traps and management*

Industry data show that the average steam trap has a service life of 4 years. This means that on average 25% of traps will fail every year, usually in the leaking position. Therefore, is imperative that every plant should have a permanent ongoing steam trap monitoring and maintenance program This can give around 3–5% boiler fuel savings. A good steam system management program can improve plant efficiency significantly. It should include self-regulating electrical tracing, condensate recovery, piping insulation, minimizing or eliminating the use of steamreducing stations and vents.

A simulation model of the Combined Heat and Power (CHP) system for the plant is the most effective tool to check the steam balance and to estimate losses. Although CHP simulation modeling is commercially available, they all lack an important feature which is data reconciliation. Aramco is currently developing in-house software to rectify this deficiency.

#### *6.4.5 Supplementary firing*

Supplementary firing may be used in combined cycles (in the HRSG) raising exhaust temperatures from 600°C (GT exhaust) to 800 or even 1000°C. Using supplemental firing will not raise the combined cycle efficiency but is used instead to increase peak power production of the unit, or to enable higher steam production in an emergency. Supplementary firing can raise the temperature of the GT exhaust gas from 800 to 900°C., enabling higher steam generation flows, pressures and temperatures.

#### *6.4.6 Boiler load management*

The performance curve for each boiler is basically a relation between fuel consumption and the steam production of the boiler. Boiler efficiencies can vary, even for nominally identical units, by 2–3%. By maximizing base load on the more efficient boilers in a set of parallel units and using the next lower efficiency boiler for swing production, overall steam gen efficiency can be increased 2–3%. Installing economizers in boilers, heat recovery from utility system blowdown, boiler minimum load reduction, minimum steam reserve reduction, and excess O2 minimization to 2%, are a few other initiatives to improve the boiler system performance. Air preheating is usually not economic, with simple payback typically exceeding 10 years.

#### *6.4.7 Minimize excess low-pressure steam*

There should never be excess LP steam at any plant site which includes fuelfired boilers. It is a symptom of gross steam system mismanagement and can be corrected using a CHP system model to pinpoint the causes of needless waste.

## *6.4.8 Minimize PRV letdown of high or medium pressure steam*

Excess HP or MP steam is a symptom of CHP system mismatch between demand and supply. In such cases, the CHP system operating and control practices should be modified to generate less steam. It can be easily done at a near-zero capital cost, so there is no excuse for plant management to allow such a situation to fester.

### *6.4.9 Recovery of water from humid boiler or furnace flue gases (condensing economizers)*

This approach was touted by academics without industrial experience back in the early 1970s in the wake of the first "energy crisis". Many got US government funding for pilot plants to demonstrate the concept. In practice, operating below the acid dew point accelerates corrosion inside the condenser. Teflon-coated internals was tried, but the coating quickly peeled off, and this approach was largely abandoned.
