The past decade has seen a global population growth of more than 700 million and with it, corresponding spikes in energy consumption and greenhouse gas emissions. As consumers and operators have made strides by introducing renewable energy options and reducing their carbon footprints, the cleaner energy alternatives of natural gas and liquefied natural gas (LNG) are expected to continue playing a vital role in the world’s energy mix, with projections that gas will supply 43% of the world’s additional demand for energy by 2040.
Today, on the heels of record supply growth and investment, the LNG sector faces exciting but uncertain times. How can we future proof a rapidly growing industry that has been around for decades? Can we do more to reduce the carbon footprint of LNG systems? And how can we use technology and innovation to further reduce the greenhouse gas emissions and thermal inefficiencies associated with the fastest-growing gas supply source in the world?
New Demand, Old Systems and Processes
The concept of liquefying natural gas dates back to the 17th century. By the early-to-mid 1900s, LNG facilities started operating primarily near centers of high demand for natural gas, and during the 1960s and 1970s, a series of LNG plants were popping up across the world.
What does all of this have to do with today’s LNG? As the industry is facing record demand, its growth is heavily dependent on legacy plants and dated equipment. Are these outdated systems and processes the best and cleanest way to grow and scale the LNG sector?
A Sector Plagued with Combustion-Related Emissions
Most existing LNG plants, especially large-scale operations (> 1 MTPA), use gas turbine drives for the main refrigeration compressors in the liquefaction process. While LNG as a whole is a cleaner option than emission-heavy alternatives such as coal, there are still many greenhouse gas emission sources involved in the LNG production chain, including fuel gas combustion emissions, flare and vented emissions, fugitive emissions, and non-routine emissions associated with start-up, shut-down or plant upset.
Similar to other sectors of the oil and natural gas industry, CO2, NOx and methane emissions from combustion devices are typically the largest contributors to total greenhouse gas emissions from the LNG process. While significant efforts have been made to improve the overall plant thermal efficiency, much more can be done.
- POINTS TO BE ADDRESSED
- Future-proofing the rapidly growing LNG industry by improving legacy plants and dated equipment
- Reducing the carbon footprint of LNG systems
- Boosting liquefaction reliability and flexibility
- KEY POINTS TO THE SOLUTIONS
- MHI’s H100 gas turbine produces more power with less environmental impact than traditional industrial gas turbines.
- A look at the H100 turbine in a Gas Turbine Combined Cycle: a 2-on-1 configuration that delivers 30% higher thermal efficiency.
- An LNG plant that uses the H100 to independently operate the Power Block and liquefaction processing equipment significantly augments the entire complex’s thermal efficiency.
- Adding the two-shaft gas turbine compressor to LNG facilities also cuts down on installation time, plant downtime and hydrocarbon gas flaring during start up, while boosting overall flexibility and reliability.
Introducing a Low-Carbon LNG Solution that Reduces Both Operational and Environmental Costs
Over the next two decades, LNG operators must meet the global energy demand in compliance with high environmental standards, while also running successful businesses. This is no easy feat. The majority of LNG plants today utilize gas turbines in simple cycle operation, which notoriously produces a lot of waste heat by venting turbine exhaust into the atmosphere.
Mitsubishi Heavy Industries (MHI) and its group companies have developed a suite of low-carbon options for LNG liquefaction, which allows operators to reduce CO2 emissions while reaping long-term operational and cost savings. MHI’s most outstanding low-carbon LNG option is the H100, a gas turbine solution aimed at reducing the carbon footprint of existing and new LNG plants.
The two-shaft industrial gas turbine produces approximately 10% more power than the often-used industrial gas turbine/helper motor package, while eliminating the complexity and minimizing the footprint and trip hazards associated with the helper motor drive systems. LNG operators can seamlessly fit the H100 to an existing plant, eliminating the major production obstacle presented by the substantial starter-helper motor associated with single-shaft gas turbines.
The H100 gas turbine gives producers the best of both worlds: 1) gas turbine efficiency similar to the largest areo-derivative engines, and 2) the power density, high reliability and low maintenance outlay typically associate with large industrial gas turbines.
The H100 in a Gas Turbine Combined Cycle: Delivering 30% Higher Thermal Efficiency
The H100 turbine plays a critical role in providing power and increasing the thermal efficiency of a well-designed Gas Turbine Combined Cycle (GTCC) Power Block. Take MHI’s 2-on-1 arrangement pictured in Figure 1. This configuration not only provides the electrical power necessary to support electric motor-driven refrigeration gas compressors in the liquefaction processing plant, it also provides the electric power needed for other users in the LNG complex. All of this is performed while delivering a thermal efficiency of approximately 30% higher than a simple cycle plant design.
Additional features of the 2-on-1 GTCC configuration include:
- The Power Block usually comes in an “N+1” configuration to allow for the off-line maintenance of a singular gas turbine. When available, a local power grid can substitute for the spare gas turbine.
- Higher availability compared to the liquefaction plants designed with simple-cycle gas turbine-driven compressors as electrical motor drivers allow for longer maintenance intervals than gas turbines.
- Electric motor drivers operate at a high-efficiency rate of 95% or more thereby contributing to the overall performance efficiency of the LNG plant; however, it is generally accepted that a transmission and efficiency loss of more than 2% must be accounted for in the overall electric motor drive package.
The H100 in a Hybrid Combined Cycle: Reducing CO2-Equivalent with a Value of ~$10MM to $20MM per year
The LNG system depicted in Figure 2 illustrates a plant in which the Power Block and liquefaction processing equipment are operated independently. In this schematic, electricity generated in the Power Block is used for motor-driven auxiliary equipment, heaters, and other components of the LNG complex.
At the same time, MHI’s H100 gas turbines are used in a similar combined cycle operation to drive the main liquefaction compressor trains. In this model, steam generated by the H100’s exhaust heat is supplied to a mechanical drive steam turbine powering one of the liquefaction process compressor trains such as the Precooled Propane compressor.
The Hybrid Combined Cycle’s recovery and repowering of waste heat significantly augments the overall thermal efficiency of the entire LNG complex. An estimated 50% of the H100’s gas turbine power can be recovered by implementing a heat recovery system. When evaluating a sample LNG plant where the order of magnitude of CO2-equivalent emissions from a refrigeration gas compression system is approximately 1-2 million tons per year and assuming the CO2 value is $35/ton, the reduction of CO2-equivalent has a value of approximately $10MM to $20MM per year.
Key features of the H100-powered Hybrid Combined Cycle LNG plant include:
- LNG production can be maintained when one of the MR compressor gas turbine drivers is scheduled for a planned outage.
- Mechanical drive gas and steam turbines are not subject to electrical losses, thus contributing to the overall thermal efficiency and a reduced carbon footprint.
- The steam turbine drive operates in conjunction with the gas turbines, which permits the system to remain in operation if one of the gas turbines undergoes maintenance.
Easy Installation, Minimal Downtime, Greater Flexibility and Ultimate Reliability
On top of delivering impressive long-term operational, environmental and financial savings, the H100 turbine comes without the installation and production headaches long associated with other traditional LNG solutions. Operators can quickly install the H-100 as a flange-for-flange replacement of older turbines, such as aging single-shaft turbines, and new equipment can be pre-staged prior to shut down to minimize installation time.
Unlike single-shaft machines, the H100 turbine and compressor package offer a range of operating speeds, which allows plants to more easily respond to variations in demand and process conditions. For example, LNG operators can slow down production at times of low demand, whereas single-shaft machines are effectively on or off, making them much less flexible.
The H100’s wide range of operating speeds also makes the turbine a particularly reliable option for owners and operators of older LNG production facilities seeking to upgrade existing facilities. The ability to reliably handle production upsets, equipment trips and bog downs makes the turbine much more appealing than single-shaft options.