Balance of Plant in an LNG Facility: The Engineering Systems That Keep the Core Running

When engineering teams and project developers evaluate an LNG facility, technical discussions almost always center on the liquefaction train - the refrigeration compressors, the Main Cryogenic Heat Exchanger (MCHE), and the mixed refrigerant circuit. This is understandable. The liquefaction train represents the largest single capital item in the facility and directly defines production throughput.

However, ask any operations manager or director of engineering what sustains reliable plant performance across years of commercial operation, and the answer returns to something less visible: the Balance of Plant, or BOP.

In the United States, LNG export capacity has expanded faster than in any other region. Gulf Coast LNG projects - from Louisiana to Texas - are setting the pace globally, while domestic small-scale and modular LNG infrastructure is growing rapidly to serve industrial fuel, marine bunkering, and heavy transportation markets. In this environment, BOP engineering has become one of the most operationally and financially consequential disciplines across the entire project lifecycle. Scope gaps during front-end loading translate directly into LNG project cost overruns, schedule impact, and reliability shortfalls that persist across the full operating life of a plant.

At RVN Inc., our LNG engineering services treat balance of plant as a core engineering scope from conceptual design through detailed engineering. Whether you are working with an LNG EPC contractor or building out an owner's engineering team, defining BOP scope correctly from day one is what separates projects that deliver on cost and schedule from those that don't.

What is Balance of Plant in an LNG facility

Balance of Plant is the collective term for all supporting systems and infrastructure outside the primary process trains that are essential for those trains to function. In an LNG facility, BOP covers the full set of utilities, safety systems, material handling infrastructure including LNG storage and loading systems, and site services that enable continuous, safe, and compliant plant operation.

If the liquefaction train is the engine of the facility, the BOP is everything that keeps that engine running - the fuel supply, the electrical grid, the cooling circuits, the safety systems, the loading infrastructure, and the site services. For US-based plant builders and operators, defining BOP scope correctly from the earliest project phases is a decision that shapes cost, schedule, and long-term operational performance.

Why BOP Engineering determines Project Outcomes

BOP systems typically account for 25 to 40 percent of total installed cost (TIC) in a grassroots LNG facility, depending on site location, plant capacity, and the extent of offsites and utilities within the project scope. For context, a Gulf Coast baseload LNG export terminal with a CAPEX in the range of several billion dollars will have BOP costs running into the hundreds of millions or a few billion dollars  a figure that deserves the same engineering discipline as the liquefaction train itself. Despite this, BOP scope definition is frequently deferred to FEED or later - one of the most consistent drivers of LNG project cost overruns between FEL-2 and project completion.

Three specific consequences follow from late BOP engagement:

• Cost growth from incomplete scope definition and late identification of long-lead items including transformers, emergency generators, and control system hardware

• Schedule compression when BOP civil works, substation construction, and underground utility installation - which frequently sit on the critical path - are under-defined going into procurement

• Reliability shortfalls when operational input is not incorporated into BOP system design, leading to equipment configurations that are difficult to maintain or operate efficiently

The right time to define BOP scope rigorously is FEL-1. For modular LNG projects in particular - where above-the-bolts BOP integration is coordinated across multiple technology packages - early scope clarity is not optional. It is the foundation of a workable LNG FEED engineering program.

Our Technology Screening and Selection service applies the same independent, criteria-driven evaluation to BOP package items - power generation technology, nitrogen generation units, and cooling system configurations - that we apply to the core liquefaction process itself.

Core BOP Systems in an LNG Plant

1. Power Generation and Electrical Distribution

LNG utilities design starts with power - and for good reason. LNG facilities carry substantial electrical loads. While refrigeration compressor drivers dominate power consumption, the broader BOP power demand is significant and must be designed with equal rigor. Key components include onsite gas turbine generators or utility grid interconnections as the primary generation source, emergency diesel generators sized to sustain critical safety instrumented systems during failures, and uninterruptible power supplies for DCS and SIS hardware.

Power system design must account for peak demand during liquefaction train startup, black-start capability requirements, and load shedding philosophy. For modular LNG facilities where electrification packages are supplied by separate vendors, BOP power system integration adds another layer of

coordination that must be resolved during LNG FEED engineering - not during commissioning and startup.

2. Fuel Gas System

Gas turbine drivers, fired heaters, flare pilots, and plant heating loads all require a conditioned, pressure-regulated fuel gas supply. The BOP fuel gas system delivers this supply reliably to all consumers throughout the operating envelope. Design elements include fuel gas scrubbers and knockout drums, pressure control and letdown stations with redundancy for critical consumers, and heat tracing where low operating temperatures create hydrate formation risk.

In US LNG facilities, the fuel gas system is commonly designed to utilize flash gas recovered from liquefaction and boil-off gas as supplemental fuel sources, reducing feed gas consumption and improving overall plant thermal efficiency.

3. Water Systems

Water systems in an LNG facility cover several distinct functions, each with its own design basis, equipment scope, and regulatory considerations. Treating water systems as a single line item in early-phase estimates is a common source of cost growth - each subsystem must be scoped and sized independently.

3.1 Raw and Potable Water

Raw water intake facilities draw from river, sea, or municipal supply depending on site location. Water treatment units process raw intake water to the quality required for potable use and equipment service. Potable water distribution supplies personnel facilities, laboratories, safety showers, and eyewash stations across the plant.

3.2 Demineralized Water

Demineralized water is produced onsite through Reverse Osmosis (RO), Electrodeionization (EDI), or ion exchange treatment systems. Demin water is used as boiler feedwater for steam generation systems and as a carrier fluid for chemical injection supply throughout the facility. Sizing of demin water units must account for peak simultaneous demand across all consumers, including startup and maintenance scenarios.

3.3 Firewater System

The firewater system is one of the most heavily regulated BOP systems on any LNG facility. NFPA 59A and FERC requirements mandate dedicated firewater supply with sufficient flow and pressure to support simultaneous operation of deluge systems, monitor nozzles, and hydrants across the largest single fire scenario defined in the facility hazard study. Firewater storage tanks must be sized for the full demand duration without relying on makeup supply. Firewater pumps - electric driven, diesel driven, and jockey pumps - are provided in a redundant configuration to ensure availability under all credible failure scenarios. Fire mains, hydrants, monitors, and deluge systems are distributed across the facility in accordance with NFPA 59A area classification and hazard study outputs.

Hydrostatic test water supply and disposal is an additional water system item frequently overlooked in early-phase estimates. Large-diameter piping and pressure vessels require significant water volumes for testing, and disposal of test water containing inhibitors must be planned and permitted well in advance of construction.

4. Cooling Water and Closed-Loop Cooling Systems

Cooling systems are a core part of LNG utilities design and one of the areas where site-specific conditions most directly shape equipment selection. LNG production generates substantial waste heat that must be continuously rejected from compressor intercoolers, lube oil systems, and process exchangers. Cooling system configuration is closely tied to site characteristics, water availability, and environmental permit requirements.

Common configurations in US facilities include aerial coolers for water-scarce inland sites, cooling towers with closed-loop recirculating systems where water availability permits, and once-through seawater cooling for coastal export terminals subject to applicable thermal discharge regulations. Seasonal ambient performance variation must be addressed in the equipment design basis during FEED.

5. Instrument Air and Utility Air Systems

Loss of instrument air is one of the most common initiating causes of unplanned plant shutdowns. Nearly every control valve, pneumatic actuator, and process analyzer in an LNG facility depends on a continuous, dry, clean instrument air supply. Reliable design requires N+1 compressor redundancy as a minimum, desiccant dryers to achieve the low dew points required for cryogenic service, and air receiver volume sized to buffer peak demand through maintenance events.

Reliability engineering for this system - compressor redundancy strategy, receiver sizing, and desiccant changeout scheduling - deserves systematic attention during detailed design. Problems with instrument air systems are among the most common causes of LNG commissioning and startup delays, yet they are straightforward to prevent with proper engineering upfront.

6. Nitrogen Generation and Distribution

Nitrogen is used throughout an LNG facility across the full range of operating conditions. Applications include purging and inerting of cryogenic piping and vessels during commissioning and maintenance, blanketing of LNG storage tanks to exclude air and prevent moisture ingress, and seal gas supply for rotating equipment in cryogenic and hazardous area service.

BOP nitrogen systems are typically built around onsite Pressure Swing Adsorption (PSA) or membrane separation units, with liquid nitrogen storage providing backup capacity. One demand scenario that is frequently underestimated in early-phase cost estimates is the nitrogen consumption during initial liquefaction train cooldown - a high-rate, finite-duration event that requires purpose-sized supply capability.

7. Flare and Pressure Relief Systems

The flare system is the primary pressure safety system of an LNG facility and one of the most heavily regulated BOP systems in the US regulatory environment. It must be designed to handle the maximum credible simultaneous relief load from defined failure scenarios including liquefaction train emergency shutdown, blocked outlet conditions, and fire case relief events.

US facilities must comply with EPA regulations under 40 CFR Part 60 governing flare design, combustion efficiency, and monitoring requirements. These obligations must be incorporated into the BOP design basis from FEL-1, not addressed as a permit afterthought.

8. Boil-Off Gas (BOG) Management

LNG in storage tanks continuously generates vapor through heat ingress from the surroundings. This boil-off gas must be continuously managed to hold tank pressure within operating limits and prevent product loss. Management strategies include BOG compressors that return vapor to the liquefaction train suction or route it to the fuel gas system, reliquefaction units in larger baseload applications, and BOG heaters and send-out systems for peak shaving facilities and truck loading terminals.

BOG compressor availability is a direct constraint on LNG loading schedules. Unplanned compressor outages restrict loading operations and can trigger commercial penalties under supply agreements. Redundancy philosophy, maintenance accessibility, and sparing strategy must be resolved during detailed design.

9.1. LNG Storage Systems

LNG storage is one of the most capital-intensive and technically specialized components within the balance of plant scope. Full containment cryogenic tanks are designed to hold liquid natural gas at approximately -162 degrees Celsius at near-atmospheric pressure. Tank configuration - single containment, double containment, or full containment - is driven by site hazard classification, regulatory requirements under NFPA 59A and DOT Part 193, required working capacity, and plot space constraints.

For Gulf Coast LNG export terminals, full containment above-ground tanks in the 160,000 to 200,000 cubic meter range are standard. For modular LNG and small-scale LNG facilities serving industrial or transportation markets, flat-bottom tanks or horizontal vacuum-jacketed vessels are selected based on throughput and footprint requirements.

Key BOP considerations for LNG storage include boil-off gas generation rates and the resulting sizing demand on the BOG management system, foundation design for cryogenic settlement, secondary containment bund sizing, and tank pressure management under varying send-out and loading rates. LNG storage system design must be integrated closely with BOG compressor sizing, the sendout and loading system, and fire and gas detection layout from the earliest stages of LNG FEED engineering.

9.2. LNG Loading and Sendout Systems

The LNG loading and sendout system is where the facility's production capacity translates into commercial delivery - and it is a BOP scope area where design gaps have direct revenue consequences.

For export terminals, the loading system encompasses marine loading arms, jetty infrastructure, vapor return lines, metering and custody transfer systems, and the associated piping and valves connecting the tank farm to the ship. Loading arm selection must account for the range of LNG carrier sizes expected to call at the terminal, the maximum allowable loading rate, and marine environmental conditions at the jetty.

For domestic distribution and peak shaving facilities, the sendout system delivers regasified LNG or direct LNG to pipeline or truck loading bays. Truck loading systems require dedicated loading islands, weigh bridges, vapor recovery connections, and overfill protection systems compliant with applicable state and federal requirements.

Custody transfer metering accuracy and proving systems are critical in both cases - these directly determine the volume of product for which the facility is commercially accountable. Metering system design must be addressed during LNG FEED engineering, not deferred as a late procurement item.

10. Fire, Gas Detection, and Safety Systems

LNG is a flammable cryogenic commodity handled in large quantities. The consequence severity of a fire or vapor cloud event demands a safety system architecture that is precisely engineered and compliant with applicable US standards from the earliest project phase.

BOP fire and gas systems include catalytic bead and open-path infrared flammable gas detectors at all credible leak sources, UV/IR flame detectors across process areas and tank dike areas, fixed water deluge and foam application systems, and an Emergency Shutdown System with hardwired safety instrumented functions certified to appropriate SIL levels per IEC 61511. US LNG facilities must comply with NFPA 59A, FERC regulations, and DOT Part 193. Siting decisions and exclusion zone calculations are shaped by these standards and must be addressed at FEL-0, before site selection and plant layout are fixed.

11. Closed Drain, Blowdown, and Slop Systems

Safe handling of hydrocarbon liquids during normal operations, maintenance, and emergency blowdown requires a dedicated closed drain and blowdown system. These systems collect liquids from equipment drains, seal vents, and relief valve discharges and route them safely to disposal or recovery. Separate warm and cold drain systems are required given the temperature extremes within an LNG facility, and heat tracing is needed on cryogenic fluid lines to prevent freezing in drain headers.

12. Control Infrastructure and Site Services

The physical infrastructure and connectivity layer of the BOP is frequently underestimated in early-phase cost estimates. This includes the Central Control Room and backup control facilities with appropriate separation and blast resistance, the Distributed Control System and Safety Instrumented System architecture, telecommunications and fiber optic cabling infrastructure, and meteorological monitoring systems required by NFPA 59A and FERC. Site roads, drainage, civil works, administration buildings, security, and access control systems round out the full BOP scope.

The RVN Approach: BOP as an Integral part of LNG Engineering

At RVN Inc., balance of plant is not treated as a scope addendum after the liquefaction train design is established. It is engineered in parallel with the core process from the earliest project stages.

Our LNG engineering services cover the full project scope from FEL-0 conceptual design through detailed engineering, including all process systems, utilities, tank farm, and loading infrastructure. For each BOP package, selecting the right technology and configuration carries the same weight as selecting the liquefaction process itself.

Our Technology Screening and Selection service applies a rigorous, independent evaluation to BOP package items - power generation technology, nitrogen generation units, and cooling system configurations - ensuring every system is matched to the client's site conditions, capacity requirements, and project economics.

Our Capital Project Engineering capabilities extend from feasibility studies through LNG FEED engineering and detailed engineering, giving plant builders and owner-operators a single, integrated team across both process and BOP disciplines.

Whether you are developing a large-scale Gulf Coast LNG export terminal, a mid-scale liquefaction facility, or a modular LNG plant for industrial or transportation fuel supply, RVN Inc. has the technical depth and project execution capability to deliver - from concept through LNG commissioning and startup.

Key Takeaways for US LNG Project Teams

• BOP scope definition belongs in FEL-1, not FEED - late definition is a leading cause of LNG project cost overruns and schedule slippage

• Instrument air, nitrogen, and power generation redundancy are high-impact reliability levers - most cost-effective to engineer correctly in early project phases

• BOG management and flare system design require early cross-disciplinary engagement between process, safety, and environmental teams

• NFPA 59A and FERC compliance shape BOP design from siting onward - regulatory engagement should not wait until permit applications are submitted

• For modular LNG projects, above-the-bolts BOP integration across multiple technology packages must be resolved during LNG FEED engineering - not during commissioning and startup

• LNG utilities design - covering power, instrument air, nitrogen, cooling, and fuel gas - carries the same CAPEX and reliability weight as the liquefaction train itself.

• LNG storage: LNG storage tanks and containment: Full containment tanks aer the standard for safety, using 9% nickel steel for inner shells that can handle up to -160C cyrogenic conditions and concrete for outer protection.

• LNG loading: In order to ensure safety and environmental compliance, the use of loading arms with Emergency Release Systems (ERS) is recommended. Also, use of quick connect and disconnect couplers is preferred.

• Operations input into BOP design reviews from FEL-2 onward is directly linked to plant reliability performance from first LNG commissioning and startup through steady-state operation

• LNG storage tanks and containment:  Full containment tanks are the standard for safety, using 9% nickel steel for inner shells that can handle up to -160C cyrogenic conditions and concrete for outer protection.

• In order to ensure safety and environmental compliance, the use of loading arms with Emergency Release Systems (ERS) is recommended.  Also, use of quick connect and disconnect couplers is preferred.