Apparatus and methods of quantum chemical analysis of phase changes in a gas flow for optimizing gas hydrate inhibitor consumption

Abstract

An apparatus and method are provided for optimizing the use of gas hydrate inhibitors by combining real-time "dew point" measurement with quantum-chemical phase-change analysis. A gas hydrate inhibitor reduces gas moisture; by measuring gas humidity and identifying the "dew type" using two chilled-mirror sensors each equipped with an imaging camera, a "dew coefficient" (0–1) is calculated via quantum chemistry analysis of inhibitor solvation. This mesoscale coefficient is used to monitor fluid phase changes. A general relationship for the water / hydrocarbon "dew coefficient" is derived as a function of changes in Gibbs free energy of dew evaporation (inhibitor solvation), gas temperature and pressure, and gas / liquid density. By combining measured "dew point" and "dew type" with quantum chemistry data of phase transformations "dew coefficient", the optimal inhibitor injection rate is determined, minimizing inhibitor consumption while preventing hydrate formation.

Description

Apparatus and Methods of Quantum Chemical Analysis of Phase Changes in a Gas Flow for Optimizing Gas Hydrate Inhibitor Consumption

[0001] The present invention relates to the oil and gas industry and more particularly to optimizing the consumption of gas hydrate inhibitors by analyzing dew point and phase changes in a natural gas stream. In gas processing, maintaining low water content is critical to avoid hydrate formation, which can block pipelines and equipment. Conventional chilled-mirror dew point analyzers measure only the gas dew point temperature and cannot distinguish between water and hydrocarbon dew in complex gas mixtures. For example, existing patents (e.g. US 4,799,235; US 4,946,288; US 5,482,371; US 8,348,500) disclose cooled-mirror sensors that use a laser beam reflected from a cooled optical surface to detect dew formation. However, these devices cannot simultaneously detect water and hydrocarbon dew in natural gas. A small change in reflected beam intensity alone cannot identify the dew type. Other approaches (e.g. IR spectroscopy in US 7,581,877 or ultrasonic and impedance methods in US 6,327,890 and US 4,948,263) measure gas humidity but do not integrate hydration chemistry or inhibitor optimization. No prior art analyzes the optimal inhibitor dosage using combined dew point measurement and quantum chemistry.

[0002] Gas hydrate formation is facilitated by small amounts of water in high-pressure (up to ~250 bar) low-temperature gas flows (down to ~240 K). Hydrates are crystalline solids of gas and water (e.g. LNG components), which can form when water condenses and freezes in pipelines, causing blockages, pressure drops, and even explosions. For example, hydrate formation has been observed in gas processing units (e.g. hydrocracker or LPG units) when dew conditions are not controlled. The usual preventive measure is continuous injection of hydrate inhibitors (e.g. alcohols, glycols) into the gas stream. However, excessive inhibitor injection is very costly, while insufficient injection allows hydrates to form. Determining the optimum inhibitor injection rate to prevent hydrates is therefore crucial. The present invention enables this determination by combining direct dew point sensing with quantum-chemical analysis of phase changes.

[0003] For the first time, the invention integrates an on-line dew point analyser with quantum chemical solvation analysis of inhibitors (alcohol or glycol) to minimize inhibitor use in oil and gas operations. The apparatus measures both water and hydrocarbon dew points simultaneously and identifies the dew composition via image processing. These measurements, together with computed changes in Gibbs free energy of dew evaporation (inhibitor solvation) at various temperatures and pressures, allow calculation of a dew coefficient that indicates the extent of phase change. Using this dew coefficient, the system computes the minimal inhibitor dosage required at the point of dew evaporation to maintain dry gas. In sum, the method achieves significant savings of chemical inhibitors and optimizes fuel / energy usage in gas fields, refineries, and petrochemical plants.

[0004] The invention provides a novel dew point measurement system and corresponding analysis methods. In one aspect, an apparatus is provided that includes two dew point sensors (one optimized for water dew and one for hydrocarbon dew) within a common explosion-proof enclosure. Each sensor has a Peltier-cooled mirror system with dedicated optics and an imaging camera. The key components of each sensor include an optical element (typically a metal mirror), a thermoelectric (Peltier) cooling module, a light source (e.g. laser or LED), a photodetector, collimating optics and lenses, and an industrial-grade imaging camera. Additional subsystems include power supplies, temperature sensors, pressure transmitters, and electronic control / processing boards. The sensors are packaged so that gas flows over the cooled optical window while the electronics remain isolated. As the mirror is cooled, vapor condenses on its surface. The reflected or scattered light pattern is captured by the photodetector and camera. By analyzing the intensity change and image of the dew formation, the system measures the dew point and determines whether the dew is water or hydrocarbon (or both). Real-time temperature and pressure of the gas adjacent to the mirror are also monitored. This allows simultaneous, online measurement of both water and hydrocarbon dew points in two-phase or high-corrosion sour gas flows. The data output from the apparatus includes the water and hydrocarbon dew point temperatures, gas moisture (relative humidity), time-lapse images and video of dew formation, and plots of light intensity versus temperature for both dew events. All data can be sent to a control room or display for further analysis.

[0005] In another aspect, quantum chemical analysis methods are used to process the sensor data and determine optimal inhibitor use. The method computes the Gibbs free energy change for evaporation of the dew under the influence of inhibitors (i.e. inhibitor solvation Gibbs free energy), and analyzes the molecular configuration of inhibitors on the dew interface. By performing a mesoscale (meso-scale) quantum analysis of the dew surface, a dimensionless dew coefficient (analogous to a coverage fraction) is calculated. The dew coefficient (ranging from 0 to 1) varies with inhibitor concentration, gas temperature and pressure, and gas / liquid density. A general formula or lookup is established for the dew coefficient as a function of ΔG (Gibbs energy of evaporation and solvation), T, P, and fluid densities. From this, the minimum inhibitor concentration needed to achieve a given dew coefficient at the observed conditions is determined. The method spans a wide range of operating conditions (including critical points) covering both water and hydrocarbon dew formation. Water and hydrocarbon dew coefficients versus temperature and pressure indicate the optimum timing and volume of inhibitor injection to minimize hydrate formation and save energy, particularly in high-pressure gas transport and production facilities. The combination of the dew point measurement results (which provide immediate phase-change data) and the quantum chemistry model (which provides the energy-based dew coefficient) yields an optimized injection strategy for hydrate inhibitors in oil and gas operations.

[0006] is a schematic block diagram of an optical dew-point sensor assembly with cooled mirror, illustrating the components (light source, cooled mirror, photodetector, amplifier, etc.) used to detect condensation (dew) by changes in reflected light intensity.is a schematic of a gas sampling and conditioning system for dew point measurement. It shows a process line and the sampling loop with isolation valves, filters ensemble, pressure regulators, flow controller, and exhaust / return / bypass flows, illustrating how a suitable gas flow is delivered to the sensor under controlled conditions.

[0007] The apparatus comprises three main subsystems: (1) the dew point sensor assemblies, (2) the electronic / processing modules (including quantum-chemistry models and computations), all shown in the, and (3) the gas sampling system which is illustrated in.  In overview, the sensors are mounted inside an explosion-proof enclosure that houses the optoelectronic hardware and data processors. Inside the enclosure, each dew point sensor is separated into three sections. At the bottom is the thermoelectric cooler (Peltier) module assembly. A sturdy metal bracket supports the Peltier cooler and serves to isolate it thermally from the rest of the sensor while distributing its heat to the enclosure interior. The Peltier device is controlled to cool a small metal mirror (optical element) mounted above it. The middle section of each sensor is the analysis cell, where the gas to be measured flows directly around the optical element. A pressure transmitter and a temperature sensor are attached to this cell. The pressure transmitter monitors the local gas pressure in real time and feeds data to the processor; this allows precise dew point measurement at varying pressures. The optical element (mirror) sits at the top of the middle section, directly exposed to the gas. When the mirror is cooled below the gas saturation temperature, condensation (dew) forms on its surface.  At the top is the protective optics housing. This houses the light source (e.g. a laser diode or LED), collimator and lenses, the photodetector for reflected light, and the industrial imaging camera. A transparent glass or quartz window separates these optical components from the gas flow. Thus the sensitive optics (light emitter, detector, camera, lenses) are shielded from the gas while still receiving reflections from the cooled mirror. The window is optically clean but gas-tight, preventing direct contact between the gas and the electronics. When dew forms on the mirror, the pattern of reflected and scattered light changes. The photodetector (e.g. a photodiode) measures the intensity of reflected light, while the camera captures real-time images of the mirror surface. The digital signal from the photodetector and the camera images are sent to processing boards inside the enclosure for analysis. Simultaneously, the temperature of the Peltier cooler module is measured (by a platinum RTD or similar sensor) and recorded. The point at which a sudden change in reflected intensity or image contrast occurs is registered as the dew point temperature. The system also recognizes whether the dew is primarily water or hydrocarbon by analyzing the image texture and intensity pattern (for example, water dew and hydrocarbon dew produce different reflectance signatures). Data is displayed on a touchscreen (e.g. a 7-inch panel) and / or transmitted to a remote receiver, including captured dew images, time stamps, and plotted signals of intensity vs. temperature

[0008] : Schematic block diagram of an optical dew point sensor. A light source (LED or laser) directs a beam onto a cooled mirror. A photodetector measures the intensity of reflected light, which drops sharply when condensation (dew) forms on the mirror. The Peltier cooler and temperature sensor control mirror temperature. An amplifier and processor analyze the signal.illustrates a typical optical dew-point sensor configuration (similar in concept to that of Kirk and Rimboi, 1975). The light source is oriented towards a reflective surface (mirror) which is attached to a Peltier cooler. As the Peltier temperature is lowered, vapor in the gas condenses on the mirror. This condensation changes the reflectivity: the photodetector output drops as the surface becomes covered with liquid. The electronic amplifier and processor (shown in the block diagram) detect this sudden change and record the corresponding temperature as the dew point. In the present invention, a similar cooled-mirror approach is used, but with added capability: an integrated industrial camera captures images of the dew as it forms, enabling distinction between water and hydrocarbon dew. The camera stream and detector signal are processed together to determine both dew point and dew type.

[0009] Gas is delivered to the sensors via a conditioned sampling system () to ensure representative and safe measurements. A portion of the main gas stream is diverted through a sampling loop. As shown in, the sample enters through an isolation valve and travels through stainless steel tubing. It first passes through filters ensemble, which removes liquid droplets, particulate matter (>1 μm), and chemical residues (e.g. residual inhibitors such as alcohols or glycols) from the gas. This filter is crucial for protecting the sensor optics from contamination and ensuring accurate dew measurements. After filtration, the gas enters a pressure regulator or series regulator to adjust the pressure to the sensor’s operating level. Depending on the application, pressure may be reduced to atmospheric or maintained at line pressure with a bypass loop (valves arranged accordingly). A pressure gauge and transmitter monitor the pressure on each sensor. The conditioned gas then flows through the dew analyser which houses the sensors assembly. Downstream of the sensor, the flow passes a flow control valve and flow indicator to maintain a constant known flow (e.g. 0.5-5 L / min recommended). Excess gas is vented or returned to the process at point. A desiccant chamber may be used if intermittent sampling is done, to keep the sampling line dry when no flow is present. The arrangement ensures that the gas reaching the sensor is at the desired pressure and free of contaminants.

[0010] illustrates the gas sampling and conditioning system schematic. A sample is taken from the main pipeline (Main Process Line) via an isolation valve and tube. It passes through a filter to remove liquids / particles, then through pressure regulators and a pressure gauge. The dew point sensor measures the sample, then the gas exits via flow control and exhaust. Additional components assist mounting and flow control.illustrates a typical piping installation for dew point measurement in a gas line (adapted from industry practice). The labeled components correspond to those described above. This ensures reliable, on-line dew point monitoring under high-pressure conditions.

[0011] The electronic subsystem includes data acquisition and control boards that read the temperature, pressure, detector, and camera signals. These boards interface with a processor that runs custom firmware and software. Importantly, the processor implements quantum chemical analysis algorithms: it calculates the dew coefficient from the dew point data and predetermined thermodynamic models of inhibitor solvation. The system references pre-computed data or equations for the dew coefficient versus temperature and pressure. Thus, when the sensor measures a dew point and detects its type, the system computes the corresponding Gibbs free energy change and dew coefficient. From this, it infers the inhibitor concentration (or injection rate) that corresponds to that dew coefficient. The software outputs the recommended inhibitor dosage or alarms if deviation from the optimum is detected. In practice, the operator or control system can use this information to adjust continuous injection of hydrate inhibitor (e.g. methanol or glycols) to the minimum required level.

[0012] In quantum chemical analysis methods of dew, the phase changes of the fluid are determined based on the changes in Gibbs free energy of evaporation (Gev) or the Gibbs free energy of liquid-to-gas transformation (ΔGlg). In this analysis, the enthalpy of dew evaporation (Qev(T) > 0) is determined as follows:

[0013] (1)

[0014] In this relation, q and m are constants of the equation, and Tc is the critical temperature of water dew under high gas pressures. Using equation (1), the changes of Gevwith respect to temperature are expressed as:

[0015] (2) where ΔGlg= ΔGs= Gg Gl, T0= 298.15 K, The numerical evaluation of Gev(T) using equation (2) is valid, since the changes in Gibbs free energy of dew evaporation at high pressures are controlled by changes in the enthalpy of the evaporation process, while entropy variations are negligible. The dew coefficient in quasi-equilibrium systems between liquid and gas phases can be evaluated in terms of thermodynamic potentials:

[0016] (3) (4) where Vland Vgare the specific volumes of the liquid and gas phases, respectively. The ratio of these specific volumes is determined through the gas and liquid densities, using equations (5) to (7).

[0017] (5) where p is the gas pressure, δ = ρc / ρ , and ρcand ρ are the critical density and density of the gas,

[0018] (6)

[0019] A is the Helmholtz free energy, and τ = Tc / T. From the numerical solution of this nonlinear equation, the gas density is determined. The dew density as a function of temperature is then calculated by:

[0020] (7) where Tc is the critical temperature, and a, b, and n are constants depending on whether the dew is aqueous or organic.

[0021] (8) By substituting equation (8) into equation (4), a general relation for the dew coefficient is obtained:

[0022] (9) which depends on gas temperature and pressure, liquid and gas densities, and the solvation effects of inhibitor molecules on the dew surface, as well as ΔGgl. The injection of inhibitors causes dew evaporation and reduces the gas moisture. Consequently, the numerical value of the dew coefficient decreases, and by minimizing this quantity, the optimal consumption of inhibitor in the gas flow is also determined.

[0023] In operation, when the dew point sensor detects condensation (water or hydrocarbon), the processor correlates the measured dew point temperature Tdpand pressure P with the quantum-analysis model. The dew coefficient βvis derived from the relation βv= f(ΔG, Tdp, P, ρl, ρg), where ΔG is the Gibbs free energy change of dew evaporation including inhibitor solvation, and ρ represents densities. A higher βv(approaching 1) indicates that most of the inhibitor is adsorbed (strong solvation), meaning less inhibitor is effectively preventing dew. A lower βv(near 0) indicates efficient inhibitor performance. The target is to operate at a βvthat corresponds to just preventing dew formation. The method produces curves of χ versus T and P (one for water dew, one for hydrocarbon dew). By plotting the current operating point on these curves, the system determines how much inhibitor is needed. For example, at a given pressure and temperature, the graph may show that βv=0.5 is achieved with X ppm of glycols or methanol in the gas; the system then recommends that injection rate. This optimization logic directly ties the measured dew conditions to inhibitor control.

[0024] All technical terms used in this description (e.g. dew point sensor, thermoelectric cooler, collimator, Gibbs free energy, solvation) are used in their conventional meaning to practitioners of optical sensing and physical chemistry. The specific materials and component examples given (e.g. mirror metals, Peltier module type) are illustrative; equivalent components and alternative sensors can be employed. The figures described above serve as one embodiment of the invention; the invention is not limited to these exact layouts or configurations.

[0025] The present invention has broad industrial use in the oil, gas, and petrochemical industries for preventing hydrate formation while conserving resources. By precisely controlling inhibitor injection, it achieves:Reduced chemical usage: Hydrate inhibitor (alcohol or glycol) injection volumes are significantly reduced while still preventing hydrate formation.Lower operational costs: Reduced inhibitor usage leads to lower chemical costs and fewer service interventions. Equipment maintenance and repair costs are decreased.Improved efficiency: Optimized process conditions improve overall energy efficiency in gas production and processing.Corrosion control: With minimal free water, pipeline and equipment corrosion rates are lowered, extending infrastructure life.Environmental benefits: Lower chemical consumption and optimized processes reduce pollutant emissions and environmental impact.Process optimization: Reduced feed gas consumption in methanol / glycol production units and improved feedstock allocation (e.g. for methanol-to-gasoline units) are enabled by better control of gas composition.

[0026] Overall, the apparatus and methods contribute to energy savings and emissions reduction by solving the problem of fuel / energy imbalance in gas extraction and processing through advanced sensing and chemistry analysis.

Claims

An apparatus for dew point measurement and dew type detection in a gas flow, comprising: an optoelectronic system including an optical element, a thermoelectric cooling module, a light source, a photodetector, an industrial imaging camera, power supply sources, temperature sensors, a pressure transmitter, electronic control boards, and one or more processors; wherein the dew point of the gas is measured by the dew point sensor and the dew type (water or hydrocarbon) is determined via image processing by integrating the industrial camera with the dew point sensor assembly within an explosion-proof enclosure.The apparatus of claim 1, wherein each of the water and hydrocarbon dew point sensors comprises a metal mirror (made of silicon, stainless steel, aluminum or copper, with or without a corrosion-resistant coating) capable of reflecting or scattering an incident laser beam on its surface depending on the type of dew (water or hydrocarbon) present.The apparatus of claim 1 or 2, wherein the combined measurement of dew point and identification of water-dew type enables determination of the dew point of two-phase fluids and highly corrosive sour gases.The apparatus of any preceding claim, wherein data output from the apparatus includes the measured water and hydrocarbon dew point temperatures, gas humidity, time-lapse images and video of the water and hydrocarbon dew formation, and plots of light intensity versus temperature for the forming dews.A method of quantum chemical analysis of phase changes in a gas flow for minimizing gas hydrate inhibitor consumption, comprising:computing changes in the Gibbs free energy of dew evaporation and inhibitor solvation;analyzing quantum phenomena at the surfaces of water and hydrocarbon dew;determining molecular configurations within the hydrocarbon dew; andcomputing a dew coefficient or mesoscale code for the hydrocarbon dew;wherein the analysis is performed over a wide range of gas temperatures and pressures (including critical conditions) that correspond to the phase changes of the water or hydrocarbon dew.The method of claim 5 or 6, further comprising plotting the water and hydrocarbon dew coefficients as functions of temperature and pressure and determining the timing for injection of hydrate inhibitors in order to minimize energy consumption in an oil production process.

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