Temperature Of Heat Carrier Research Articles

Process characteristics investigation of simulated circulating fluidized bed combustion combined with coal pyrolysis

A poly-generation process of simulated circulating fluidized bed (CFB) combustion combined with coal pyrolysis was developed in a laboratory scale. Pyrolysis characteristics of three bituminous coals with high volatile contents were investigated in a fixed bed with capacity of 10 kg solid samples. The effects of initial temperature of solid heat carrier, pyrolysis holding time, blending (ash/coal) ratio and coal particle size on gas and tar yields were studied experimentally. The results indicate that the initial temperature of the heat carrier is the key factor that affects the gas and tar yield, and the gas composition. Most of the gas and the tar are released during the first few minutes of the pyrolysis holding time. For caking coal, the amount of char agglomerating on the pyrolyzer inner wall is reduced by enhancing the blending ratio. The experimental results may provide basic engineering data or information for the process design of CFB combustion combined with coal pyrolysis in a large scale.

QUALITY ASSURANCE FOR HOT WATER SUPPLY FROM DH SYSTEM: SIMULATION TOOL AND APPLICATION

Widely developed DH systems in Lithuanian towns and small settlements undergo modernisations aimed to increase their efficiency and heat supply quality. Typically, modernisations include the replacement of building heat substations, the reduction of heat losses in pipes and more efficient heat production, including the use of indigenous fuel resources. It was notified that new heat substations equipped with automatic heating control devices have backward impact on the technological parameters of DH networks. Modelling tools for simulation of hydraulic and thermal parameters in the network allow estimating of potential deviation of heat carrier temperature with loading variations not only during the season of the year, but also over day and night. Special technical measures can be taken to avoid unduly low heat carrier supply temperatures and violation of hot water supply quality requirements. Cost estimation of such measures versus the option of full network renovation is presented in the article.

Derivation of efficiency factors for uneven irradiation on a fin absorber

In the equation for thermal energy output from a flat-plate solar collector (written as a function of the collector mean heat carrier temperature), both the gain and the loss terms are multiplied by the collector efficiency factor, F ′. For a concentrating collector with an uneven (non-uniform) irradiation on the absorber, the efficiency factor for the gain term, here called the optical efficiency factor, F ′ c, is different from F ′ and is a function of the irradiation distribution on the absorber. If the heat loss coefficient is assumed to be constant across the fin, the optical efficiency factor for absorbed irradiation at a certain distance from the edge of the absorber is independent of absorbed irradiation at other locations and can therefore be expressed F ′ c( x), where x is the distance from the edge of the absorber. Close to the edge, F ′ c( x)< F ′ and close to the pipe, F ′ c( x)> F ′. In this paper formulas are derived for calculating F ′ c( x) for a fin absorber with constant fin thickness. By weighting F ′ c( x) with the absorbed irradiance, S c( x), and integrating across the absorber, an absorber average optical efficiency factor, F ′ c,a, is obtained. This value replaces F ′ in the gain term of the equation for thermal energy output. If, instead, the energy output equation is expressed as a function of the inlet temperature, F ′ c,a can be used for calculating a corresponding heat removal factor for uneven irradiation, F R, c . Formulas for calculating the temperature distribution across the absorber for the case of uneven irradiation are also derived.

Control and energy metering in low temperature heating systems

A new approach of temperature control and energy metering in low temperature heating (LTH) systems is presented. The required heat is supplied in terms of energy pulses by intermittent operation of the circulation pump. The control unit calculates the heat demand from external variables basically represented by the ambient air temperature. The parameters necessary for temperature control can be extracted when the heat transfer coefficient and the heat capacity of the floor construction are known. Furthermore, the control strategy opens for energy metering in LTH systems by means of the parameters heat carrier temperature and the duty cycle. The method is demonstrated to be at least accurate within ±5%.

Analysis of the Errors of Heat Measurements in an Open Heat Supply System

An analysis is made of how the error of heat measurement depends on the variation of the flow transducer uncertainties and the error in measurement of the heat carrier temperature for various differences of that temperature in the supply and return lines.

Analytical solution to the problem of heat interaction of fluid flow and solid filling

The results of analytical solution to the problem of thermal interaction of a fluid stream with a media of solid particles found on the basis of the ODTPM model [1] are presented. A non-stationary behaviour of the volume-averaged temperature of solid filling, being a measure of the efficiency from heat transfer between fluid and solid phases, and of the heat-carrier temperature at the exit of the layer is studied. Time dependences computed according to the obtained relationships are in good agreement with the results of numerical calculations [1] for different sets of the problem parameters. The found solution expands the possibilities to analyze the efficiency of the “fluid-solid phase” systems and can be a basis to develop methods of experimental evaluation of different parameters of the system.

Low-temperature convector made from polymeric material for heat-pump applications

With a view to reducing the operating temperature of air heaters, a convector consisting of a plate heat-transfer matrix, placed at the bottom of an enclosure acting as a chimney, was designed and tested. An inexpensive polymeric material (polypropylene) was selected for the heat-transfer plates to achieve a lightweight low-cost unit. An appropriate computer program was used to optimize the prototype convector and to evaluate the influence of the main geometric and operational parameters: plate spacing and height; chimney height; heat carrier temperature and rate. The performance of the unit subsequently fabricated, measured in a thermostatic test chamber, was in good agreement with the theoretical predictions. As an example, an output of 1.2 kW was obtained for a mean water temperature of 41°C with a convector volume of 0.22 m 3, two-thirds of which was occupied by the chimney. The convector exhibited a good thermal output even when fed at very low water rates, thus achieving a thorough cooling of the incoming water. The convector performance could be enhanced by resorting either to higher chimneys or to a mechanical draught. In the latter case, it is shown theoretically that a small fan's power consumption (say 5 W) is sufficient to at least double the natural convection output, provided the heat-transfer matrix is re-optimized.

Interchannel heat-carrier mixing with periodic flow-rate variation over time in spiral-tube bundles

The nonsteady results of investigating the nonsteady heat-carrier mixing in bundles of spiral tubes with periodic variation in air flow rate by heat diffusion from a central group of electrically heated tubes are outlined. The frequency and amplitude of flow-rate oscillation influence the variation in heat-carrier temperature and effective turbulent-diffusion coefficient. The transition from steady thermal conditions to conditions with regular periodic variation in the temperature and the relative coefficient of heat-carrier mixing for the given type of nonsteady hydrodynamic conditions is considered.

ダウンフロー方式による石炭の急速熱分解（Ｉ） 太平洋炭の急速熱分解

A coal pyrolysis and combustion combined system, which aims at recovering gaseous and tarry liquid products by pyrolysis of coals as well as heat (electric power) by combustion of all chars produced, is considered to become a feasible first step to promote effective use of coal resources.From the standpoint, a rapid pyrolysis of coals is being studied in a down-flow reactor which is heated by a high temperature sand; this is because high caloric gaseous and tarry liquid products can be effectively recovered from coals.In the present study. Taiheiyo coal was rapidly pyrolysed to clear relation between pyrolysis conditions (pyrolysis temperature, length of heating section and temperature of heat carrier), product distribution (yield of produced gas, tar and chars) and the properties of the products.1. Yields of chars decreased while those of gases increased, with increasing of pyrolysis temperature and length of heating section. A maximum tar yield was shifted to higher pyrolysis temperature in a shorter length of heating section, and was estimated to 30% in the pyrolysis temperature of 600-650°C in a longer length of heating section, because tars produced were secondarily pyrolysed.2. Rapid pyrolysis of a sample coal was finished in a second order. Maximum pyrolysis rates depended on pyrolysis temperature.3. Rapid purolysis of a sample coal was not effected with temperature of sand as a heat carrier.4. Combustibility of chars produced was considered not so different from a sample coal because they had higher caloric values and was, not coagulated in a pyrolysis step.5. Gaseous products were composed of H2, CH4, CO. CO2, and C2-C4 hydrocarbon gases. They had high caloric values of 5, 000-8, 500 kcal/Nm3.6. Elemental and NMR analyses of tars produced showed that the properties changed from paraffinic to aromatic with progress of the secondary pyrolysis followed by increase of pyrolysis temperature. They had caloric values of 6, 000-7, 500kcal/kg.

Application of KhG type of electric pump for pumping viscous heat carriers

The authors attempted to widen the range of use of leakproof monoblock electric pumps of the type KhG by studying the scope of application of the 1.5KhG-3A-2.8-3 electric pump in a liquid heat supply system (LHS) working with a viscous heat carrier in the thermal zone (TZ) of an oscillating screw mixer. The temperature of heat carrier was measured by thermoelectric transducers mounted at the outlet of the electric pump. The proposed starting procedure widens the area of application of KhG type pumps for pumping organosilicon heat carriers having a kinematic viscosity of not more than 10/sup -4/ m/sup 2//sec and a specific heat of not less than 1.7 kJ/kg./sup 0/K at the ambient temperature.

Adaptive nonisothermal computer control of a batch reactor

The adaptive temperature control method of reaction mixture in a batch reactor with strongly exothermic reaction is verified experimentally. The utility degree of cooling capacity of the reactor is kept on the required value by use of a two-position controller which is changing the flow rate of heat carrier into the cooler. The method is based on continuous identification of properties of the system in actual time by use of the Hewlett-Packard 3 052 A computer centre. During the experiments temperature of mixture in the reactor and temperature of heat carrier in the cooler were measured. From the obtained data and their time derivatives reactivity of the mixture, heat transfer coefficient and utility degree of cooling capacity of the reactor were evaluated. In the experiments were studied the effects of cooler inertia and of additive noise in the temperature measurement on safety and quality of control. Experimental results have proved that the method is applicable to control of reaction temperature even under conditions when properties of the system are changing significantly e.g. reactivity of the mixture and dynamic properties of the manipulated variable and when pseudostationary states of the reactor are unstable in the open control loop. They simultaneously point to a significant effect of noise on system identification.

Strengthening freshly pressed dinas green compacts for the purpose of automating their transportation

Automation of removal of freshly pressed dinas compacts from presses and stacking of them on furnace carts may be done only with a significant increase in the strength of the corners and edges of the compacts. Sufficient strengthening of the angles and edges of freshly pressed dinas compacts may be provided with a short heat treatment for a moisture content of not more than 3%, even with the addition to the mixture of a normal production lime-iron mixture consisting of milk of lime (2.5% by CaO), iron-containing additions (0.8% by Fe2O3), and sulfite-yeast mash (0.8% by dry residue) and pressing of the compact to an apparent density of not less than 2.24 g/ cm3. A short heat treatment of freshly pressed dinas compacts at a heat carrier temperature of not less than 150°C for strengtening of them is promising for mechanization and automation of transportation of the compacts from the presses and loading of them on the furnace carts. Consideration of the question of the design and construction of an automated production line for the transportation of freshly pressed dinas compacts from the presses to the tunnel furnaces must be advanced from the stage of laboratory experiments to the stage of production testing. The development and testing of the proposed variation of automation of transportation of freshly pressed dinas compacts from the presses and their heat treatment, stacking in the elements of the charge (columns), and placing on the furnace carts would, in addition to the reduction in labor costs, significantly reduce dust production in the press-dryer-tunnel furnace area.