(72f) Optimal Use of Design Constraints for Efficient System Design

Optimal use of Design Constraints for Efficient System Design

Zeeshan Farooq, Mahmoud Bahy Nour Eldin and Omar Rajeh, Energy System Division, P&CSD Saudi Aramco, Dhahran

This is competitive world and with ever increasing energy prices the industrial communities are invited to conserve energy resources. Designing any system is having many constraints and if we utilize the imposed constraints in a way to improve the system efficiency. It is like hitting two birds with one stone. As any system design is defining its efficiency by operation you can achieve the design efficiency but you cannot improve further without changing system design. So, if a system is designed for higher efficiency will perform always superior that an inefficient designed system. Proper system design is prerequisite for higher efficiency achieved in the systems though operating it in best possible manner is also important to achieve designed efficiency but higher efficiency cannot be achieved by operating an inefficient designed system. Any system design is driven by requirements from the design and the constraints imposed on the system either by process requirements, environment norms, material limitation, economics etc.

In this paper we have system consists of Water Injection Pumps (WIPs) driven by Gas Turbines (GTs) utilizing Sales Gas (sweet gas) as fuel and the GTs exhaust is utilized for Heat Recovery Steam Generators (HRSGs) and the exhaust flue gas from HRSGs are designed for 400⁰F. This high exhaust temperature is used as the back-up fuel gas (sour gas) is not sweet and in emergency case when fluid Sales Gas is not available it can be used to run the WIPs as well as plant. A new system is proposed to produced MP steam by utilizing heat in the flue gas, which can be switch back to the current system i.e. exhaust at high temperature when Sales Gas is not available and sour gas is used as fuel. In order to maximize the savings the produced MP steam is used for inlet cooling to the GTs and remaining steam is utilized for Condensing turbine to produce electricity.

This case study demonstrate that huge savings are possible when we use the design constraint up to the limit as in present case the constraint utilized in the current design is exhaust flue gas temperature of 400⁰F. In the proposed initiative it was split into two constraints lower exhaust temperature of 150⁰F when Sales Gas is utilized as fuel and higher exhausts temperature of 400⁰F during emergency when sour gas is used as fuel. The propose system is fulfilling design constraints as well as providing higher efficiency and more value to the fuel used to run WIPs.