Liquid Heat Transfer Media Research Articles

Modelling and validation of energy systems with dynamically operated Power to Gas plants for gas-based sector coupling in de-central energy hubs

Participants of the COP 26 summit have agreed to limit global temperature rise to 1.5 K by 2050. Out of the many strategies envisaged to meet the targets of COP 26, the ‘Sector Coupling’ process aims to use renewable electricity in residential heating, chemical industry, and transportation sectors. Several studies predict that de-central energy systems will play a significant role in the future. Among the proposed sector coupling strategies in de-central energy systems, the Power to Gas (PtG) process producing chemical energy carriers like Substitute Natural Gas (SNG) from renewable power is gaining acceptance. Numerical models of de-central energy systems are needed to analyse sector coupling under fluctuating renewable energy generation and changing gas demand. This study introduces a numerical model of a decentral energy system that includes a novel methanation concept developed at the Engler Bunte Institut of KIT called 3 Phase Methanation. Here, H2 from electrolysis and CO2 from DAC or other biomass-based sources are passed through a slurry bubble column reactor. The slurry is a suspension of the catalyst in a liquid heat transfer medium where the heat of the reaction is dissipated. The 3-Phase methanation process is modelled in this study using the axial dispersion method. Earlier studies describing experimental campaigns conducted on the pilot plant in KIT have proven that the reactor core is nearly isothermal with stable product gas compositions even if the load changes are instantaneous. In this study, it is shown that the numerical model can replicate the experimental results. Following modelling and validation, the numerical model of the PtG plant is integrated with the other components to simulate the de-central energy system. The simulation results demonstrate the dynamic output of all the components and, in particular, the response provided by the PtG plant. This model can be adapted to simulate sector coupling in future de-central energy systems and analyse aspects like long-term energy storage, GHG minimisation and cost-optimal operation.

Using CFD to improve the performance of a heat exchanger from a gasifier

In this paper, a Computational Fluid Dynamics (CFD) analysis is performed on a gas-liquid heat exchanger fitted on a gasification equipment. The flow and temperature patterns are preliminary investigated using SolidWorks Flow Simulation software, in order to gain insight into the involved physical processes, and to find the exchanger weak points before being manufactured and tested. The analysed equipment tranfers heat from the flue gasses generated by a gasification system, towards a liquid heat transfer medium. This is subsequently sent to a second liquidliquid heat exchanger used to heat water from a boiler. As a result of the analysis, solutions aiming at performance improvement of the equipment are discussed and proposed.

ENSURING STABLE OPERATION OF GAS COLLECTION SYSTEM IN CONDITION OF REDUCED WELL PRODUCTION

Any gas condensate field has an extensive gas collection system (GCS), through which gas is delivered from the wells to a Gas Processing Plant by means of reservoir energy. At the final stage of field development the GCS operating conditions undergo significant changes, in particular due to lower temperature of transported gas and increased water cut in the production fluid. In winter, simultaneous action of these factors may lead to formation of ice and hydrate plugs disrupting normal operation of the GCS. Gas stream velocity shall exceed so-called critical velocity to ensure that the flowlines operate in the liquid removal mode. Its value is determined by a pipeline diameter, ratio of gas and liquid density, thermobaric conditions, flowline slope and other factors. Ensuring necessary velocity at the final stage of operation is usually impossible, thus, complete moisture removal is problematic and the hazard of ice formation persists. This paper proposes an innovative technology providing stable GCS operation by preventing ice formation in the flowline. For that end, the gas-liquid mixture in the GCS gets additional heat from heat tracing located inside the GCS. The heat tracing is coiled tubing with constant circulation of liquid heat-transfer medium: methanol-water solution, heated by rejected heat when passing through the air cooler unit (ACU). The coiled tubing forms a closed loop with the methanol pipeline. Changes in heat exchange medium consumption are introduced with a VSD-driven pump, basing on the results of temperature measurement in the flowline. Application of the proposed technique allows not only providing emergency-free GCS operation, but recuperation of rejected heat from the ACU as well.

Selection of flue-pipe diameter for crude heaters with an intermediate liquid heat-transfer medium

Results are presented for a computational analysis performed to determine the most favorable diameters of the high-temperature section of the flue pipe in crude heaters with an intermediate heat-transfer medium. It is demonstrated that economically suitable diameters for the flue pipe are limited by the minimum value for which the working expression was obtained in the study. It is also indicated that ring-vortex generators placed in the high-temperature section of the flue pipe for intensification of convective heat exchange are technically and economically expedient. Heaters with flue pipes (1), in which one or several flue pipes and an efficient coil are placed in a single housing filled with an intermediate liquid-heat-transfer medium (usually water), are employed to heat crude for its transport and hot processing of water-oil emulsions for industries. The burning of fuel and transfer of the heat of the combustion products through the walls of the pipes to the inter- mediate heat-transfer medium, and through the walls of an efficient coil to the products being heated take place in the high- temperature section of the flue pipes. Heaters with an intermediate liquid heat-transfer medium provide a "soft" regime for heating of crude, and the fire safety required. Their drawbacks are cumbersomeness and high metal consumption due to the existence of two heat-transfer sur- faces: the flue pipe and the tubes of the efficient coil. The diameter of the high-temperature section of the flue pipe is one of the most important parameters affecting the layout solution devised for development of the heaters, and their weight and clearance dimensions. The flue processes that take place in this section proceed at a high rate, and no large volume of flue space is required for their accomplishment. The limiting process that determines the volume of the high-temperature section of the flue pipe and the surface area of its walls is the heat exchange of the combustion products of the fuel. As a result of this process, the combustion products should be cooled to 600-1000°C prior to the inlet to the con- vection (low-temperature) section of the flue pipe (2). The effect of the diameter of the flue pipe on the rate of heat exchange of combustion products of the fuel is dual in nature. An increase in the diameter and a corresponding increase in the thickness of the radiating layer of combustion products

PV-hybrid and thermoelectric collectors

Two different principles of thermoelectric cogeneration solar collectors have been realized and investigated. Concerning the first principle, the thermoelectric collector (TEC) delivers electricity indirectly by first producing heat and subsequently generating electricity by means of a thermoelectric generator. Concerning the second principle, the photovoltaic-hybrid collector (PVHC) uses photovoltaic cells, which are cooled by a liquid heat-transfer medium. The characteristics of both collector types are described. Simulation modules have been developed and implemented in TRNSYS 14.1 (1994), in order to simulate their behaviour in typical domestic hot-water systems. The discussion of the results shows that the electric output of the PV-hybrid collector is significantly higher than that of the thermoelectric collector.

Comparisons of paraffin wax storage subsystem models using liquid heat transfer media

In this work three models are presented which describe the thermal behaviour of a paraffin wax thermal store powered by a liquid type heat transfer fluid. The first model ignores all internal temperature gradients leading to the asymptotic best possible performance. The performance of real heat exchangers is using the second model described herein. This model incorporates the effects of natural convection as well as conduction governed by the growth of either a liquid film barrier during melting or a solid film barrier during freezing. Simplifications derived from the detailed model lead to a third model which retains sufficient detail about the mode and mechanism to enable a rapid yet accurate prediction of system results without the higher computational effort. Comparisons of all three models are made by means of a reference example where the use of a paraffin wax multiple day store in a solar assisted domestic hot water system is considered. The results verify the validity of the third simplified model although the results do not suggest that wax could replace water as a storage medium for this application.

Analyse fonctionnelle de l'echangeur thermique a flux imposé

The problems posed by the extraction of high heat-fluxes in heat-exchangers with imposed flux (notably in nuclear reactors) lead to a search for the maximum volumetric performance which is consistent with maintaining the temperature of the hottest point below a temperature limited by safety considerations. In the case of a uniform heat flux and a liquid heat-transfer medium the author shows that this becomes a matter of choosing the minimum values for a coefficient of transport and heat by the fluid, a coefficient of transfer by convection and a coefficient of transfer by conduction across the heating material and its container. The author recalls the dependence of these coefficients on the geometry of the system, the physical properties of the fluid and its flow-rate. This last parameter makes it necessary to introduce the pumping power per unit volume, which must be limied to reasonable values. A table shows the influence of the various parameters on the coefficients introduced and on the pumping power and allows a comparison of the advantages of the usual cooling liquids. In the case of a boiling heat-transfer medium the transport term disappears (the volumetric coefficient of transport becomes infinite) and the coefficient of transfer by convection has a high value in nucleate boiling but decreases drastically on the appearance of critical dry-out or “burn-out”, which is dangerous in most circumstances. Coupling between the transport of heat and pressure-drop is the cause of various types of instability which may bring about “secondary burn-out”. Finally, the author examines the effect of longitudinal or transverse variations in the thermal flux.

The Thermosludge Water Treating and Steam Generation Process

Abstract The Thermosludge process internally softens and makes high-pressure steam directly from hard and saline oilfield or other water. Pilot plant and early full-scale plant work established several physical and chemical principles found necessary or desirable for good operation, and for control and practical elimination of scale on the process heating surfaces. These principles are use of a secondary liquid heat transfer medium, provision of time and space for water chemical reactions ahead of the boiling zone, and presence of sludged reaction products throughout the boiling zone. Other pertinent factors are discussed such as dissolved and suspended solids limits, foaming, corrosion, and heat transfer. Introduction In 1964 considerable use of steam in California oil fields was beginning to cause shortages of good steam generator feedwater in some areas. It seemed evident that in some situations oilfield brine or other low-quality water would have to be used to generate high-pressure steam directly. The Thermosludge process was developed to meet this need, and early results of its field use have been reported previously. This article discusses both pilot plant and full-scale plant design and operation particularly relative to the high-temperature reactions and scaling characteristics of some of the chemicals present in the waters. Present understanding of the process should allow broader use in its original field, and in other processing areas dealing with difficult waters. Pilot Plant Design and Operation After considerable study of chemical and engineering factors involved, a pilot plant program was set up. Three main theories or principles believed to lead to successful operation were followed in the pilot plant design and the same principles were carried into the full-scale plant design. First, heat should be applied via a secondary fluid heat transfer medium rather than directly in a combustion space. Relative to direct-fired beating, the secondary fluid heating guarantees that maximum tube wall temperature will be well within the allowable metal temperature limit regardless of local scaling or salting up. Many situations call for soluble salt in the steam generator in concentrations of as much as 15 percent by weight perhaps half of the limiting solubility. Even if conventional tube scaling were somehow entirely prevented, such situations would require the inherent heat flux control of a secondary heat medium to prevent gross fouling and plugging by salt deposits. Second, means should be provided in terms of high-temperature time and volume to preheat and chemically react the feedwater before it enters the boiling zone. The practicality of this is based on the expectation that thermally induced mineral sludging reactions will proceed much faster and more completely in the 350 to 600F environment than, for example, in the conventional lime-soda process. Thus, the feedwater should be entirely softened by the time it arrives at the boiling zone.