Essentials of Oil and Gas Utilities

Process Design, Equipment, and Operations

Alireza Bahadori

• Publisher: Gulf Professional Publishing
• Year: 2016
• ISBN:
  9780128030899
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Every oil and gas refinery or petrochemical plant requires sufficient utilities support in order to maintain a successful operation. A comprehensive utilities complex must exist to distribute feedstocks, discharge waste streams, and remains an integrated part of the refinery's infrastructure. Essentials of Oil and Gas Utilities explains these support systems and provides essential information on their essential requirements and process design. This guide includes water treatment plants, condensate recovery plants, high pressure steam boilers, induced draft cooling towers, instrumentation/plant air compressors, and units for a refinery fuel gas and oil systems. In addition, the book offers recommendations for equipment and flow line protection against temperature fluctuations and the proper preparation and storage of strong and dilute caustic solutions. Essentials of Oil and Gas Utilities is a go-to resource for engineers and refinery personnel who must consider utility system design parameters and associated processes for the successful operations of their plants.

• Discusses gaseous and liquid fuel systems used to provide heat for power generation, steam production and process requirements
• Provides a design guide for compressed air systems used to provide air to the various points of application in sufficient quantity and quality and with adequate pressure for efficient operation of air tools or other pneumatic devices.
• Explains the water systems utilized in plant operations which include water treatment systems or raw water and plant water system; cooling water circuits for internal combustion engines, reciprocating compressors, inter- cooling and after-cooling facilities; and "Hot Oil" and "Tempered Water" systems

Chapter 1

Fuel systems

Abstract

Fuel systems are necessary to provide the proper fuel for a variety of users in the plant. They should include facilities for collection, preparation, and distribution of fuel to users. Alternative fuels (as required) should be made available at all consuming points. The commonly used ones are liquid fuel and gas fuel. On liquid fuel supplies at least one pump and its standby should be steam driven or available reliable other power sources. Standby pumping units should be arranged for instantaneous start-up on the failure of the operating unit. This chapter specifies the requirement for process design of fuel systems used in oil and gas processing industries. Major design parameters and guidelines for process design of fuel systems are discussed.

Keywords

liquid fuel

gaseous fuel

LPG vaporizer

gas turbine fuel

refinery gasoline fuel

fuel selection

The increasing demand for energy and the continuing increases in prices for standard fuels demand greater flexibility in the use of fuels in gas turbines.

Besides the standard fuels natural gas (typical heating values between 39 and 46 MJ/kg) and Diesel No. 2 fuel oil (42 MJ/kg), there is an increasing interest in low-BTU gases, synthetic gases (syngas here), and even liquid fuels (eg, heavy fuel oil, Naphtha, and condensates).

Low-BTU gases refer to fuels with heating values between 10 and 35 MJ/kg. Syngas denotes synthetically produced gases that generally have even lower heating values (LHVs), between 4 and 12 MJ/kg. This chapter specifies the essential requirements for process design of fuel systems used in oil- and gas-processing industries and outlines the major design parameters and guidelines for process design of fuel systems. It covers both gaseous and liquid fuel systems.

1.1. Fuel-supplying systems

As the need for higher efficiency power plants increases, a growing number of combined-cycle power plants are incorporating performance gas fuel heating as a means of improving overall plant efficiency. This heating, typically increasing fuel temperatures in the range of 365°F/185°C, improves gas turbine efficiency by reducing the amount of fuel needed to achieve desired firing temperatures. For fuel heating to be a viable method of performance enhancement, feedwater has to be extracted from the heat recovery steam generator at an optimum location. Boiler feedwater leaving the intermediate pressure economizer is commonly used. Using gas-fired, oil-fired, or electric heaters for performance gas fuel heating will not result in a power plant thermal efficiency improvement.

Proper design and operation of the gas fuel heating system is critical to insure reliable operation of the gas turbine. Improper selection of components, controls configuration, and/or overall system layout could result in hardware damage, impact plant availability, and create hazardous conditions for plant personnel.

This chapter addresses the critical design criteria that should be considered during the design and construction of these systems. Fuel should be used to provide heat for power generation, steam production and process requirements.

Fuel systems are necessary to provide the proper fuel for a variety of users in the plant.

A fuel system should include facilities for collection, preparation, and distribution of fuel to users.

Alternative fuels (as required) should be made available at all consuming points. The commonly used ones are liquid fuel and gas fuel. One liquid fuel supplies at least one pump and its standby should be steam driven or available via other reliable power sources. Standby pumping units should be arranged for instantaneous start-up on failure of the operating unit.

Low-pressure users are items such as boilers, fired heaters, and reciprocating engines. High-pressure users are gas turbines. All fuel systems need to be kept free of solid contaminants that can plug instrumentation and fuel nozzles. In addition, fuel streams need to be maintained above the hydrocarbon dew point to prevent any liquid slugs in the fuel users.

The following section identifies general system requirements that apply to all gas fuel heating systems. These requirements, in addition to those described in the combustion specific system requirements section shall be followed during the design and development of the system. Gas fuel supplied to the gas turbine shall meet the particulate requirements. If the components in the gas fuel heating system are constructed of materials susceptible to corrosion, a method of final filtration upstream of the gas turbine interface is required. Particulate carryover greater than that identified in the standards can plug fuel nozzle passages, erode combustion hardware and gas valve internals, and cause damage to first stage turbine nozzles. The new gas piping system must be properly cleaned prior to initial gas turbine operation. Additional design considerations are those related to gas fuel cleanliness. The fuel delivered to the gas turbine must be liquid free and contain a specified level of superheat above the higher of the hydrocarbon or moisture dew points.

Saturated fuels, or fuels containing superheat levels lower than specified, can result in the formation of liquids as the gas expands and cools across the gas turbine control valves. The amount of superheat provides a margin to compensate for temperature decrease due to pressure reduction, and is directly related to incoming gas supply pressure. (Note: within this document, gas fuel heating strictly for dew point considerations is still considered to be in a “cold” state. Heating for performance purposes is considered “heated” fuel.) The design of the gas fuel heating system shall prevent carryover of moisture or water to the gas turbine in the event of a heat exchanger tube failure. Water entrained in the gas can combine with hydrocarbons causing the formation of solid hydrocarbons or hydrates. These hydrates, when injected into the combustion system, can lead to operability problems, including increased exhaust emissions and mechanical hardware damage. Proper means of turbine protection, including heat exchanger leak detection, shall be provided.

Gas being supplied to the gas turbine interface point shall meet the minimum gas fuel supply pressure requirements as defined in the proposal documentation. These minimum pressure requirements are established to insure proper gas fuel flow controllability and to maintain required pressure ratios across the combustion fuel nozzles. The gas fuel heating system shall be designed to insure that these requirements are met during all modes of operation over the entire ambient temperature range. The design of the gas fuel heating system shall insure that the design pressure of the gas turbine gas fuel system is not exceeded.

Overpressure protection, as required by applicable codes and standards, shall be furnished. In addition to minimum and maximum pressures, the gas turbine is also sensitive to gas fuel pressure variations. Sudden drops in supply pressure may destabilize gas pressure and flow control. Sudden increases in supply pressure may potentially trip the turbine due to a high temperature condition. Limitations on pressure fluctuations are defined in the gas turbine proposal documentation.

The gas fuel heating system shall be designed to produce the desired gas fuel temperature at the interface with the gas turbine equipment. Guaranteed performance is based on the design fuel temperature at the inlet to the gas turbine gas fuel module. The gas fuel heating and supply systems shall compensate for heat losses through the system. Compensation shall include but not be limited to elevated heater outlet temperatures, use of piping and equipment insulation, and minimization of piping length from heater outlet to turbine inlet. The gas fuel heating system shall be designed to support specified gas fuel temperature set points required by the gas turbine. These set points include high and low temperature alarms, gas turbine cont...