Parabolic Trough Concentrator Research Articles

04/02947 Direct steam generation in parabolic trough concentrators with bimetallic receivers: Flores, V. and Almanza, R. Energy, 2004, 29, (5–6), 645–651

04/02947 Direct steam generation in parabolic trough concentrators with bimetallic receivers: Flores, V. and Almanza, R. Energy, 2004, 29, (5–6), 645–651

Degradation of toluene and acetaldehyde with Pt-loaded TiO 2 catalyst and parabolic trough concentrator

Photocatalytic degradation of volatile organic compounds (VOCs) with Pt-loaded TiO 2 was analyzed at elevated temperatures in the laboratory experiments (40–190 °C) and in the field experiments (30–230 °C). The temperature of catalyst coated on the sunlight receiver was easily elevated to around 200 °C by parabolic trough concentrator (1 m × 1 m). When gaseous toluene (15 ppm) or acetaldehyde (400 ppm) was passed through the reactor, 79% of toluene or 93% of acetaldehyde was removed continuously. In the similar condition, bare TiO 2 was rapidly deactivated by the formation of byproducts. The combination of sunlight concentrator and Pt–TiO 2 catalyst exhibited the enhancement of complete degradation of VOCs, the inhibition of deactivation, and the reactivation of photocatalyst. The contributions of photocatalytic and catalytic activities of Pt–TiO 2 were analyzed by using UV lamp and electric heater. Acetaldehyde is thermocatalytically degraded by photodeposited Pt on TiO 2 at 70–190 °C without UV irradiation, however the UV irradiation is necessary for the complete oxidation of acetaldehyde into CO 2. It is inferred that the degradation of VOCs is enhanced by the combined effect of Pt thermocatalyst and Pt–TiO 2 photocatalyst.

Solar photoreactors comparison based on oxalic acid photocatalytic degradation

Solar heterogeneous photocatalytic degradation of oxalic acid in water is carried out in four different solar photoreactors: a parabolic trough concentrator (PC), a tubular collector (TC), a compound parabolic collector (CPC), and a V-trough collector (VC). The reactors operate under equal conditions of solar irradiance, collection surface and fluid flow rate to ensure a better comparison between the systems. The effects of TiO 2 catalyst concentration and radiation incidence angle on the degradation are studied. Oxalic acid degrades without appreciable generation of intermediates, and a simple kinetic model is proposed to describe the process. There are differences in the degradation rates depending on the collector geometry. The CPC shows the best overall performance in terms of accumulated energy, followed closely by the VC. Incidence angle affects the total amount of energy collected but does not reduce very much the efficiency of the reactors to use this energy in the photocatalytic process.

Degradation of toluene and acetaldehyde with Pt-loaded TiO2 catalyst and parabolic trough concentrator

Degradation of toluene and acetaldehyde with Pt-loaded TiO2 catalyst and parabolic trough concentrator

Solar photoreactors comparison based on oxalic acid photocatalytic degradation

Solar heterogeneous photocatalytic degradation of oxalic acid in water is carried out in four different solar photoreactors: a parabolic trough concentrator (PC), a tubular collector (TC), a compound parabolic collector (CPC), and a V-trough collector (VC). The reactors operate under equal conditions of solar irradiance, collection surface and fluid flow rate to ensure a better comparison between the systems. The effects of TiO 2 catalyst concentration and radiation incidence angle on the degradation are studied. Oxalic acid degrades without appreciable generation of intermediates, and a simple kinetic model is proposed to describe the process. There are differences in the degradation rates depending on the collector geometry. The CPC shows the best overall performance in terms of accumulated energy, followed closely by the VC. Incidence angle affects the total amount of energy collected but does not reduce very much the efficiency of the reactors to use this energy in the photocatalytic process.

Direct steam generation in parabolic trough concentrators with bimetallic receivers

This document shows the results obtained in direct steam generation for low powers in parabolic trough concentrators with bimetallic Cu–Fe wall receivers. The objective is to study its thermal behavior under transient conditions and stratified two-phase flow. Experimental results in transient state appear considering the variants of mass flows between 60 and 150 kg/h, the direction of the solar beam irradiance on the receiver is from below and on one side of the receiver, this last being the most critical, in particular in steel receivers because of low thermal conductivity. Some conclusions in this work are that the most significant deformation is in a transient state and it happens only in one part of the receiver, when it changes from the liquid phase to the steam phase during the boiling process. The bimetallic receiver reduced the transient deformation to the degree that it does not seem a problem for some critical parts of the absorber system during the direct steam generation (DSG). Whereas in steel receivers the deformation rises to 7 cm, in the Cu–Fe receivers the most drastic deformation was only of 18 mm upwards with a mass flow of 150 kg/h and wall temperature of 200 oC. So, the use of the bimetallic receiver is recommended for the DSG for low power applications.

Behavior of the compound wall copper–steel receiver with stratified two-phase flow regimen in transient states when solar irradiance is arriving on one side of receiver

Direct steam generation (DSG) in parabolic trough concentrators can cause some instabilities in steel absorbers. These instabilities are caused mainly along the stratified two-phase flow related to the boiling process of water. These instabilities are manifested as a transient state and shown as a bending of the absorber, causing a rupture of the glass envelope of the receiver. This bending has been associated with the thermal gradient produced by the boiling of water, and the effects are related to the thermal conductivity of the absorber, the flow pattern and heating of the absorber from below around solar noon. When solar beam irradiance is arriving on one side of the absorber, the bending, which is always upwards, can be up to 50 mm. This is the worst condition because the temperature difference is at its maximum at a transient state. This paper presents the results of a bimetallic absorber (copper–steel), which should reduce such deflections due to the high thermal conductivity of the copper and the mechanical resistance of the steel. In order to compare the results of the theoretical model with experimental results, it was necessary to build a bimetallic absorber 3 m long with a 31.7 mm internal diameter and a thickness of 2.6 mm. The bending obtained experimentally was between 5 and 10 mm, depending on the mass flow and the temperature difference in the wall receiver. As a main conclusion, the bending of the receiver is acceptable, eliminating the rupture of the glass envelope, and it may be used in DSG of parabolic trough collectors at low flows. The objective of this work is to apply DSG to low power generation with parabolic trough plants.

Technical feasibility and economic viability of a small-scale grid connected solar thermal installation for electrical-energy saving

This paper reports on the techno-economic assessment of a grid-connected solar thermal system used for electrical-energy saving in the residential sector. The technical characteristics of the solar thermal system, based on a line-focus parabolic-trough concentrator, are given and its useful electrical and thermal-energy production is estimated using a simulation program based on a Monte Carlo method for reading solar radiation data. The economic assessment is performed using the Life-Cycle Savings (LCS) method and the payback period (PBP) of the investment's initial capital cost is determined.

DSG Under Two-Phase and Stratified Flow in a Steel Receiver of a Parabolic Trough Collector

The bending of a receiver tube in two-phase flow under stratified conditions when water is first introduced to the hot steel receiver of a 14.5-m long parabolic trough concentrator is presented in this paper. Thermal gradients were observed on the absorber wall at the inlet of the receiver tube during the boiling of water, at low mass flow of 1.6×10−5m3/sec (1 liter/min), and low pressure 4×102kPa. It should be noted that the solar concentrator was focused on the receiver tube, which contained static air before the water was introduced. The introduction of the water produced a change in the temperature difference between the upper and lower sides of the receiver, from 40-60 K to much lower temperatures, in about 45 seconds. The bending of the steel receiver tube occurred when the two-phase flow began. Maximum deflection was observed when the thermal gradient reached a minimum value. We conclude that, when the flow of steam, water, and air exist in a stratified pattern, the combination of these three elements produces the bending phenomenon. The theoretical model, developed to evaluate the experimental data, confirms that the change in temperature gradient produces the bending of the steel receiver tube during this transient stage.

Parabolic trough reflector manufactured with aluminum first surface mirrors thermally sagged

This project was conceived with the aim of developing a parabolic trough concentrator with first surface solar mirrors made over floated soda-lime glasses with concave geometry. In order to cover all the surface of the concentrator, whose measurements were 2.37 m of aperture and 1.14 m long, 16 mirrors were built with sizes of 0.3×0.6 m and they were put together like a mosaic set. Each mosaic segment of the parabolic trough was fabricated using a male mold over which were made concave mass-rock (Masa-roca ®) parts of the same size of the mirrors. This product works up to 800°C with a minimum deformation when it has been set and hardened. In order to sag the floated glasses, they were introduced in a furnace up to 600°C for about 2 h. Mirrors were made using sputtering technique with planar magnetron. The evaporation of aluminum film was about 1000 Å in thickness, while SiO 2 was about 3000 Å. The specular reflectance of the mirrors was around 86%. The field test of focusing such a concentrator gave a size focus of about 5.08 cm, where over 90% of reflected beam solar irradiance arrived on a simulated pipe receiver with this diameter.

Design and thermal analysis of a two stage solar concentrator for combined heat and thermoelectric power generation

A design procedure and thermal performance analysis of a two stage solar energy concentrator suited to combined heat and thermoelectric power generation are presented. The concentrator is comprised of a primary one axis parabolic trough concentrator and a second stage compound parabolic concentrator mounted at the focus of the primary. The thermoelectric device is attached to the absorber plate at the focus of the secondary. A cooling tube is fitted to the cold side of the thermoelectric device to extract the waste heat and maintain a high temperature gradient across the device to improve conversion efficiency. The key requirements of the concentrator design are to be tolerant of tracking misalignment, maintain temperature gradients to suit thermoelectric generation and minimise heat losses. A design methodology is presented which allows interception of rays within an angular region ±δ . This results in a wider receiver for the parabolic trough concentrator than would usually be used for a similar concentration ratio. The role of the second stage concentrator in limiting heat losses from the absorber plate is evaluated. Results indicate that in addition to improving the concentration efficiency, the second stage compound parabolic concentrator of the proposed design also inhibits convective air movement and, consequently, improves the overall performance of the solar concentrator.

Optical flux measurements in the focal area of a parabolic trough concentrator

Optical flux measurements in the focal area of a parabolic trough concentrator

Developments in solar photocatalysis for water purification

Photocatalytic processes in the presence of titanium dioxide provide an interesting route to destroy hazardous organic contaminants, being operational in the UV-A domain with a potential use of solar radiation. In this paper, some specific contaminant classes of interest such as ethylbenzene, γ-lindane and EPTC have been tested at laboratory scale and in the field to determine the feasibility of the photocatalytic oxidation of organic contaminants in water.Our preliminary results at laboratory scale with these chemicals have provided a better understanding of the photocatalytic process which seems to be efficient and not selective. The application of these processes in removal of γ-lindane from water operating in a parabolic trough concentrator has demonstrated to be effective, being possible to reduce 99.9 % of γ-lindane levels in water in acceptable times.

Solar steam generating systems using parabolic trough concentrators

Solar steam generating systems using parabolic trough concentrators have been in use for the past decade in several countries in the world. During the past years, various R & D efforts have been put into use to improve the performance. This paper reviews various aspects of solar steam generating systems and the operational problems that were encountered by various users of these systems.

Effect of optical errors on flux distribution around the absorber tube of a parabolic trough concentrator

Using simulation techniques, the effect of optical errors on the flux distribution around absorber tubes of Parabolic Trough Concentrators (PTCs) were investigated. It is found that the total optical error has profound effect on the intercept factor, as well as on the optical efficiency of PTCs.

Simple structure for parabolic trough concentrator

A simple welded frame structure for parabolic trough concentrators suitable for developing countries is described. Static load tests were conducted on this structure to study its deflection characteristics under various load conditions. The results show that the slope error of the reflector support, corresponding to normal wind loads were found to be within the specified limits, and the structure withstood the load corresponding to extreme wind load conditions.

Design data for the computation of thermal loss in the receiver of a parabolic trough concentrator

The design data required for the computation of thermal loss in the receiver of a parabolic trough concentrator for specific absorber tube diameters, various ambient temperatures, wind velocity and absorber temperatures from 50 to 350°C in steps of 10°C are presented in this paper. Curve-fitting equations for the above and a few empirical relations are also presented to enable the designer to generate the required data for any absorber temperature, absorber diameter, ambient temperature, wind velocity and emissivity of the solar selective coating of the absorber.

A choice of the position of receiver with photocells in parabolic trough concentrator

The uniformity of the distribution of flux density on the solar receiver along the perimeter of different forms of its inner channel cross-sections was studied. The receiver being an element of parabolic trough concentrator (PTC) is intended to work with cooled photovoltaic cells installed on it. A method for calculating the power of concentrated flux on the plane surfaces, which are oriented in different ways with respect to the PTC focus, was developed. A situation was found in which a satisfactory uniformity of flux was received. The investigation was fulfilled for the conditions of the currently developed Kislovodsk's photovoltaic solar power plant.

Parabolic trough concentrators—design, construction and evaluation

A brief review on the design aspects of the structural, optical and thermal subsystems of parabolic trough concentrators is given. Existing methods of performance evaluation and techniques to improve their performance are also discussed.

Operation and performance of the solar steam generation system installed at the government silk factory, Mysore

A solar steam generation system that generates steam at a temperature of 150°C is in operation at the Government Silk Factory, Mysore. The system uses parabolic trough concentrators to heat pressurized water which flashes to steam in a flash boiler. The steam thus produced is fed into the plant steam mains for use in several processes in the printing section. The performance of the system has been continuously monitored. The collector field has delivered energy to the flash boiler at an average daily efficiency of 45–53%. The average daily efficiency of the system is 33.5%. The daily and hourly values of energy collected and steam generated on a clear day in April are presented as well as a monthly summary for that month.