Natural Gas Pretreatment & Pressure Regulating System for Gas Turbine Power Plant

Project Overview

1. Project Background

Large gas turbines require a large quantity of clean natural gas supplied to them on a continuous basis. The gas supplied to modern power generation turbines must be conditioned in terms of impurity removal and pressure stabilization. Frequently, the natural gas supplied via transmission pipelines also includes moisture in the gas stream which must be removed as well. Mercury & sulfur compounds, which are routinely found in natural gas supplies also require removal. This gas conditioning must be achieved at large flow rates at high pressures to support efficient, safe, and reliable turbine operation.

Pacific Energy Company Limited was constructing a major power generation facility utilizing 10 GE 9E heavy-duty gas turbines and required a natural gas pretreatment and pressure regulating system to supply gas of the required quality. High-volume natural gas flow rates needed to be pretreated and the downstream pressure required to be stabilized in order to satisfy the operating specifications of the turbines.

Our engineering team created a customized high-capacity natural gas pretreatment station to support reliable natural gas supply for ongoing power generation.

2. Operating Conditions & Technical Parameters

Natural Gas is supplied from the upstream high-pressure pipeline. It will require filtration, pressure reduction, and distribution control prior to use in the turbine fuel system.

Key design parameters are as follows:

• Application: Natural Gas Supply for Gas Turbine Power Plant
• Gas Turbines: 10 × GE 9E
• Design Flow Rate: 420,000 Nm³/h
• Inlet Pressure: 5 MPa
• Outlet Pressure: 1.9 – 3.1 MPa

The system provides constant pressure and clean natural gas supply to the turbine units, irrespective of unit load.

3. Customer Challenges

When the project was first conceptualized, the client was faced with a host of technical difficulties related to the initial design.

• Ultra-High Gas Flow Requirement:
  The total fuel gas demand for ten GE 9E class gas turbines is extremely high and requires pretreatment systems that can handle a flow of 420,000 Nm³/h without undue pressure drop or restriction.
• Strict Fuel Gas Quality Requirements:
  Gas turbines are a highly sensitive piece of equipment that can be adversely affected by contamination in the fuel supply. Common contaminants encountered within fuel supplies include dust, water, and other pipeline impurities which, if not removed, could damage the turbine’s fuel nozzles and reduce combustion efficiency.
• Stable Pressure Control:
  The test pressure in the upstream flow path was 5 MPa. The turbines required a regulated supply pressure between 1.9–3.1 MPa. The test article had to perform under varying loads to meet these test objectives.
• High Reliability for Continuous Operation:
  Power plants typically run around the clock; therefore, it is critical that the fuel gas system be designed to operate 24/7 with high reliability and safety, with as little downtime as possible.

4. Our Customized Solution

To meet the client’s needs, Baker Hughes developed a high-capacity natural gas pretreatment and pressure regulating skid to include filtration, pressure management, and safety interfaces.

• High-Efficiency Gas Filtration:
  Multi-stage filtration and separation units remove bulk solids, pipeline solids, and condensate liquids from natural gas streams, resulting in gas of turbine fuel quality and protecting costly turbine components from damage.
• Multi-Stage Pressure Regulation:
  The Pressure Regulator Unit is designed to reduce the upstream pressure from 5 MPa to a specific operational pressure range of 1.9–3.1 MPa and maintain the pressure stable through all conditions including load variations.
• Balanced Gas Distribution System:
  The system provides an evenly balanced gas flow distribution to the 10 GE 9E gas turbines, allowing for consistent gas turbine combustion and performance.
• Integrated Safety Protection:
  The Station is provided with slam shut valves, pressure relief devices, and associated monitoring.

5. Equipment Operation Performance

After commissioning, the supplied natural gas pretreatment station has been operating stably and around the clock on full load in the operation of the power plant. The station operates on designed gas supply volumes of 420,000 Nm³/h with a high-quality outlet pressure in the range of 1.9–3.1 MPa while oscillations in load on the turbine are ignored.

The multi-stage filtration system removes solid particles and pipeline contaminants to ensure that natural gas supplied to the 10 GE 9E gas turbines is of the correct fuel gas quality.

Key operational results include:

• Stable Pressure Control: The pressure regulating system consistently maintains stable outlet pressure in the face of variable pipeline pressure.
• High System Reliability: The station is designed for 24/7 power generation with the station operating stably and with low maintenance requirements.
• Improved Turbine Protection: Clean and dry fuel gas eliminates the potential for nozzle clogging and reduces the risk of combustion instability.
• Uniform Gas Distribution: The gas pressure reducing station provides uniform fuel gas supply pressure to all 10 turbine units resulting in uniform combustion and turbine output.

Since start-up, the plant has operated stably and efficiently and has lived up to our expectations in delivering a consistent and reliable supply of fuel gas to the power generation portion of our plant on an ongoing basis for extended periods of time.

6. Core Advantages of the System

• Designed for Large-Scale Power Plants: The system can handle extreme high gas flow rates and requires precise pressure control.
• High Reliability and Safety: The Redundant Protection Devices and industrial-grade components ensure long-term stable operation in the power plant environments.
• Skid-Mounted Modular Design: The pretreatment equipment is installed as a modular skid-mounted unit which simplifies transportation and installation of the pretreatment equipment and facilitates quick and easy commissioning.
• Reduced Maintenance Requirements: The system is designed for easy access to the filtration components and valves, in order to reduce maintenance time and operating costs.

7. Customer Benefits & ROI

The installed natural gas pretreatment system provided the company with improved safety and operating efficiencies and achieved significant cost savings.

• Improved Turbine Efficiency: A clean and stable supply of fuel gas is crucial to achieving optimum combustion quality within GE’s 9E turbine type, allowing for maximum efficiency in power generation.
• Reduced Equipment Wear and Maintenance Costs: Cleaning impurities from the fuel system and turbine avoids damage to these components, reducing maintenance and the associated cost of spare parts.
• Enhanced Plant Reliability: Maintaining stable pressure ensures a constant supply of fuel gas to the turbine, avoiding trip events and maximizing plant availability.
• Faster Investment Payback: TerraPura power has successfully optimized the design of the system and reduced the overall risk to operations, resulting in a lower life of project cost and increased reliability of power. This will help accelerate the ROI of the entire project.

8. Typical Application Scenarios

This solution is widely used in:

• Gas-fired Power Plants
• Natural Gas Transmission Stations
• LNG/CNG Facilities
• Petrochemical Industries