Hans Müller-Steinhagen

Heat Transfer Fouling: 50 Years After the Kern and Seaton Model

Fouling of heat exchangers is a chronic problem in processing industries. In addition to the appropriate selection of operating conditions and exchanger geometry, there are numerous chemical and mechanical methods to mitigate fouling and to remove deposits from the heat transfer surfaces. However, all methods to reduce fouling require some understanding of the mechanisms of the deposition process and of the structure and adhesion of deposits on the heat transfer surfaces. Almost exactly 50 years ago, D. Q. Kern and his co-author, R. E. Seaton, published a paper attempting to describe the growth of fouling deposits in terms of an unsteady-state heat and mass balance for the heat transfer surface. More or less at the same time, the TEMA fouling resistances were published based on operational and anecdotal evidence of fouling for a range of heat exchanger applications. These two approaches have since formed the basis for most heat transfer fouling models and heat exchanger designs. Increased costs of energy, raw materials, and production downtime have contributed to the growing interest in heat transfer fouling. More recently, environmental legislation has put additional pressure on fouling-related CO2 emissions and disposal of cleaning chemicals. Despite these efforts, fouling of heat exchangers is still far from been understood in its whole complexity. The present paper documents the 2009 D. Q. Kern Award Lecture in which some selected aspects of fouling research to date have been presented and areas have been identified where significant research and development activities are still required.

Numerical Simulation and Experimental Analysis of a Modular Storage System for Direct Steam Generation

Thermal energy storage is a key technology for the commercialization of solar thermal power plants. This paper gives an overview of a coupled system comprised of concrete regenerators and latent heat storages for direct steam generation, as developed by the German Aerospace Center. Methodologies for an effective transient numerical description of the heat conduction processes inside the single modules and in the whole storage system are presented and their validity is proven by experiments. The presented process has a nominal system pressure of 105.6/80.0 bar for charging/discharging; the corresponding boiling temperatures are 315/295°C. As storage material of the latent heat storage, sodium nitrate with a melting point of 305°C is applied. With the presented models, a prediction of the storage systems temperatures, capacities, and effectiveness is possible. As a result, the design of a 1000-MWhth storage system is presented.

Economic Potential of Innovative Receiver Concepts With Different Solar Field Configurations for Supercritical Steam Cycles

The cost reduction potential of solar power towers (SPT) is an important issue concerning its market introduction. Raising the steam process temperature and pressure can lead to a cost reduction due to increased overall plant efficiency. Thus, for new receiver configurations a supercritical steam cycle operated at 300 bar / 600°C / 610°C live steam conditions was assumed. The considered systems include innovative direct absorption receivers, either with conventional or beam down heliostat field layouts. For the beam down option the receiver is assumed to be a cylindrical vessel with a flow-through porous absorber structure at the internal lateral area of the cylinder. The direct absorption receiver option consists of a cylindrical barrel with downwards oriented aperture, whose absorber structure at the internal lateral area is cooled by a molten salt film. For the assessment, CFD based methods were developed to be able to examine the receiver efficiency characteristics. Based on the receiver thermal efficiency characteristics and the solar field characteristics the annual performance is evaluated using hourly time series. The assessment methodology is based on the European Concentrated Solar Thermal Roadmap (ECOSTAR) study and enables the prediction of the annual performance and the levelized cost of electricity (LCOE). Applying appropriate cost assumptions from literature the LCOE were estimated for each considered SPT concept and compared to tubular receiver concepts with molten salt and liquid metal cooling. The power level of the compared concepts and the reference case is 200 MWel. The sensitivity of the specific cost assumptions was analyzed. No detailed evaluation was done for the thermal storage, but comparable storage utilization and costs were assumed for all cases. At optimized plant parameters the results indicate a LCOE reduction potential of up to 0.5% for beam down and of up to 7.2% for the direct absorption receiver compared to today’s state of the art molten salt solar tower technology.

Economic Chances and Technical Risks of the Internal Direct Absorption Receiver

Increased receiver temperatures of solar tower power plants are proposed to decrease the plants levelized electricity costs (LEC) due to the utilization of supercritical steam power plants and thus higher overall plant efficiency. Related to elevated receiver temperatures preliminary concept studies show a distinct LEC reduction potential of the internal direct absorption receiver (IDAR), if it is compared to liquid in tube (LIT) or beam down (BD) receiver types. The IDAR is characterized by a downwards oriented aperture of a cylindrical cavity, whose internal lateral area is illuminated from the concentrator field and cooled by a liquid molten salt film. The objective is the further efficiency enhancement, as well as the identification and assessment of the technical critical aspects. For this a detailed fluid mechanic and thermodynamic receiver model of the novel receiver concept is developed to be able to analyze the IDAR’s operating performance at full size receiver geometries. The model is used to analyze the open parameters concerning the feasibility, functionality and performance of the concept. Hence, different system management strategies are examined and assessed, which lead to the proposal of a cost optimized lead-concept. This concept involves a rotating receiver system with inclined absorber walls. The spatial arrangements of the absorber walls minimize thermal losses of the receiver and enhance film stability. The centrifugal forces acting on the liquid salt film are essential to realize the required system criteria, which are related to the maximal molten salt temperature, film stability and droplet ejection. Compared to the state of the art at a 200 MWel power level the IDAR concept can lead to a LEC reduction of up to 8 %. The cost assumptions made for the assessment are quantified with sensitivity analysis.

11th International Conference on Heat Exchanger Fouling and Cleaning—2015, Enfield, Republic of Ireland

Deposit formation occurs in most chemical, desalination and power generating processes. This is mainly due to the nature of the involved fluids which frequently contain components that may precipitate to form various deposits on heat transfer surfaces. Depending on thickness and thermal conductivity, such deposits can greatly reduce the performance of the apparatus. This widespread phenomenon is associated with significant environmental impact, additional energy consumption leading to 1–2.5% of global CO2 emissions, and reduced production. The cost penalties due to fouling in heat exchanger applications alone have been estimated as about 0.25% of the GDP of industrialized countries.

Economic Chances and Technical Risks of the Internal Direct Absorption Receiver (IDAR)

Increased receiver temperatures of solar tower power plants are proposed to decrease the plants levelized electricity costs (LEC) due to the utilization of supercritical steam power plants and thus higher overall plant efficiency. Related to elevated receiver temperatures preliminary concept studies show a distinct LEC reduction potential of the internal direct absorption receiver (IDAR), if it is compared to liquid in tube (LIT) or beam down (BD) receiver types. The IDAR is characterized by a downwards oriented aperture of a cylindrical cavity, whose internal lateral area is illuminated from the concentrator field and cooled by a liquid molten salt film. The objective is the further efficiency enhancement, as well as the identification and assessment of the technical critical aspects. For this a detailed fluid mechanic and thermodynamic receiver model of the novel receiver concept is developed to be able to analyze the IDAR’s operating performance at full size receiver geometries. The model is used to analyze the open parameters concerning the feasibility, functionality and performance of the concept. Hence, different system management strategies are examined and assessed, which lead to the proposal of a cost optimized lead-concept. This concept involves a rotating receiver system with inclined absorber walls. The spatial arrangements of the absorber walls minimize thermal losses of the receiver and enhance film stability. The centrifugal forces acting on the liquid salt film are essential to realize the required system criteria, which are related to the maximal molten salt temperature, film stability and droplet ejection. Compared to the state of the art at a 200 MWel power level the IDAR concept can lead to a LEC reduction of up to 8%. The cost assumptions made for the assessment are quantified with sensitivity analysis.Copyright

10th International Conference on Heat Exchanger Fouling and Cleaning—2013 Budapest, Hungary

The heat exchanger fouling and cleaning community is confronted with new challenges that have not been foreseen in the past and with old problems that are increasingly getting worse. For example, the automotive industry utilizes more heat exchangers to meet efficiency and emission standards by reducing NOx through exhaust gas recirculation (EGR) coolers. While theoretically very effective, this technique has been severely hindered by rapid formation of various types of deposit on the cooler surfaces. Along the same lines, oil refineries nowadays have to cope with heavier crude oils or densified residuals with higher risk of fouling from sources that until recently have not been economical to process. World population growth, particularly in arid areas, demands more potable water, which is mainly produced from seawater, which in thermal desalination units is prone to the chronic formation of deposits. Numerous studies have shown that heat exchanger fouling may be responsible for 1–2.5% of global CO2 emissions. Cost penalties due to fouling, for example, for additional fuel, down-time, overdesign, cleaning chemicals, and so on, have been estimated as about 0.25% of the gross domestic product (GDP) of industrialized nations.

Development of a mobile, stand-alone test facility for solar thermal collectors and systems

Testing of solar thermal systems and components requires different standards and thus different test facilities. Usually each facility is individually designed and constructed for tests according to a specific test method. For performing tests of solar thermal systems and collectors according to the most popular standards, test laboratories or manufactu-rers have to invest a huge amount of staff time, resources and capital to set up the required test facilities.