Why measure Vapour Pressure?

What is Vapour Pressure?

Vapour pressure is the pressure exerted by a vapor in equilibrium with its liquid (or solid) phase at a given temperature.

Here’s the key idea:

In any liquid, molecules are constantly moving. Some have enough energy to escape the surface and become vapor.
At the same time, vapor molecules can collide with the liquid surface and re-enter it.
When the rate of evaporation equals the rate of condensation, the system reaches equilibrium, and the pressure of the vapor at this point is the vapour pressure.

Vapour pressure increases with temperature because more molecules have enough energy to escape the liquid.
Liquids with higher vapour pressure at a given temperature evaporate more easily (more volatile).
When vapour pressure equals the surrounding atmospheric pressure, the liquid boils.
Vapour pressure depends only on temperature and the substance’s properties, not on the volume of liquid or container size.

Refineries:

Crude Oil: Vapour pressure is a critical factor in crude oil blending because it impacts safety, transportation, refining,
compliance, and operational costs. High vapour pressure increases the risk of vapor formation, which can lead to fires or
explosions during handling, storage, and transport. It also dictates transportation requirements, influencing the design of pipelines, tankers, and the need for specialized safety measures. In refining, vapour pressure guides the selection of processing strategies to efficiently separate crude components, while in blending, it ensures that combined crude streams achieve desired volatility and performance characteristics without exceeding safety limits. Regulatory agencies often mandate specific vapour pressure thresholds—particularly for rail transport—to reduce environmental and safety risks. Accurate measurement and control of vapour pressure not only help meet these requirements but also minimize the potential for costly accidents, equipment damage, and operational downtime.

Refined Products: Vapour pressure plays a critical role in safety, quality control, and regulatory compliance in the petroleum industry. From a safety perspective, high vapour pressure can cause vapor lock in fuel systems, particularly in hot weather or at high altitudes, and can create hazards in the transportation and storage of crude oil and petroleum products by increasing the risk of pressure build-up, leaks, or explosions. It is also closely linked to a liquid’s boiling point, helping determine safe handling temperatures. In quality control, vapour pressure is a key parameter in gasoline blending, with lower summer values reducing evaporative emissions and higher winter values aiding cold starts. It is also used to evaluate crude oil quality, optimize refining strategies, and ensure products meet specifications set by industry standards. From a regulatory standpoint, vapour pressure measurement is essential for emission control, as it directly affects evaporative emissions contributing to smog, and is subject to government limits to protect environmental and public health.

BARTEC's P700 online physical property analyzers correlates with ASTM standards, and offering features such as optional validation sample systems, stream switching, and TVP output.

LNG Facilities:

Vapour Pressure Measurement on C4 Splitter Towers

At LNG facilities, accurate vapour pressure measurement on C4 splitter towers is vital for ensuring consistent product quality, optimizing operational efficiency, and maintaining stringent safety and regulatory standards. Continuous monitoring of vapour pressure guarantees that butane and other C4 fractions meet exact volatility specifications required for downstream processing, blending, and direct sale, which helps prevent off-spec products, protect customer relationships, and maximize value.

From an operational standpoint, real-time vapour pressure data enables precise control of temperature and pressure within the splitter tower, enhancing separation efficiency, improving recovery of valuable hydrocarbons, and reducing energy use while avoiding costly process interruptions. Maintaining vapour pressure within safe limits also reduces the risk of over-pressurization, vapor lock, and accidental release of flammable gases, protecting both personnel and equipment. Additionally, consistent vapour pressure monitoring supports compliance with environmental and safety regulations by ensuring products meet mandated volatility limits for transport and storage, helping LNG facilities avoid fines, shutdowns, and reputational damage.

BARTEC's RVP-4 is a versatile, low-maintenance online vapor pressure analyzer that directly measures critical quality properties of petroleum products—such as gasoline, natural gas liquids, and crude oil—across various temperatures and pressures, compliant with ASTM methods D5191 and D6378, to ensure safe storage, transportation, environmental compliance, and optimized refinery operations.

LPG Facilities:

At LPG and natural gas condensate facilities, controlling vapor pressure is critical to producing stable, marketable liquid hydrocarbons that can be safely transported and stored under atmospheric conditions. Crude oil and condensate often contain dissolved light gases—such as methane (C1), ethane (C2), and propane (C3)—that increase volatility and vapor pressure. Removing these light hydrocarbons through a stabilization process reduces vapor pressure to acceptable levels, typically between 9 and 12 PSIA, ensuring the liquid product meets safety, handling, and specification requirements. Accurate vapor pressure measurement during this process is essential for operators to confirm that volatile components have been sufficiently stripped out, maximizing liquid recovery while maintaining product stability.

The stabilization process typically involves passing the hydrocarbon liquids through a stabilizer column or fractionation system where volatile light ends are separated and removed as vapor, while heavier components such as butanes (C4) and pentanes (C5) are retained in the liquid phase. This controlled separation increases the economic value of the final products by preserving heavier hydrocarbons in liquid form, which generally command higher prices than their gaseous counterparts. Vapor pressure measurement guides the operation of these stabilizer units by providing real-time data that helps optimize temperature and pressure settings, ensuring the product remains within specification limits. Ultimately, consistent vapor pressure control and stabilization improve facility safety, protect product quality, and maximize profitability in LPG and condensate operations.

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