Heat Cleaning Research Articles

14th Heat Exchanger Fouling and Cleaning Conference - 2022, Wagrain, Austria

14th Heat Exchanger Fouling and Cleaning Conference - 2022, Wagrain, Austria

Economic and Environmental Implications of Fouling in Crude Preheat Trains

The economic, environmental and safety consequences of fouling are the key reasons for industrial and research interest in heat exchanger fouling and cleaning. The implication of fouling in crude oil refineries has changed in the recent decades due to better monitoring tools, use of fouling mitigation devices, optimization of the use of antifoulants, optimization of process conditions, better blending of crudes, better design of heat exchangers and selection of exchanger tube materials. This brings a need for the economic impact of fouling in crude refinery preheat train to be revisited. The estimation of the cost of fouling in crude preheat train is discussed via updating the assumptions previously used in literature. The updated fouling cost estimate for the crude preheat train in the US refining sector is likely to be in the range of 1–1.2 B US$ per year for 2019. It is shown that the cost of fouling needs to be associated with a relevant refining profit or a crude refining margin as it is possible for the refinery to processes crudes with higher fouling problems after compensating the fouling cost with the price of the crude.

Standard versus combined chemical, mechanical, and heat decontamination of hospital drains harboring carbapenemase-producing organisms (CPOs): A randomized controlled trial.

We sought to determine whether combined chemical, mechanical, and heat cleaning was superior to standard cleaning for the decontamination of 32 sink and shower drains harboring carbapenemase-producing organisms (CPOs). Of 16 intervention drains, 10 (63%) were decontaminated until day 7 versus 1 (5%) of 16 comparator drains (P = .002). Intensive cleaning may be useful if administered repeatedly in drain-associated CPO outbreaks.

Chemical, Mechanical, and Heat Cleaning to Decontaminate Hospital Drains Harboring Carbapenemase-Producing Enterobacteriales

Background: Carbapenemase-producing Enterobacteriales (CPE) outbreaks have been linked to contaminated wastewater drainage systems in hospitals. The optimal strategy for CPE decontamination of drains is unknown. In this randomized controlled trial, we aimed to determine whether combining chemical, mechanical, and heat cleaning was superior to routine cleaning for drain decontamination. Methods: We enrolled CPE-contaminated hospital drains at 2 geographic locations. Eligible drains were those initially found to be culture positive in a 2017 study and that remained positive (by RT-PCR) when retested twice in August 2018. Drains were stratified by type (sink versus shower) and randomized with a 1:1 allocation ratio (as per computer-generated randomization) to standard-of-care cleaning (comparator) or combined chemical, mechanical, and heat cleaning (intervention) on day 0. Drain tail pieces were swabbed on days 0 (before administration of the intervention), 1, 2, 3, 7, and 14, and at months 1, 2, 3, 4, 5, and 6. Swabs were placed into brain heart infusion with 10% Dey-Engley neutralizing broth and incubated overnight. Direct RT-PCR was performed to detect KPC, VIM, NDM, OXA-48–like, IMP, GES, and SME genes. The primary outcome was drain decontamination, defined as no detectable carbapenemase gene in the drain from day 1 to 7 (inclusive). Results: Overall, 33 CPE-contaminated drains were enrolled (7 sink and 26 shower); 17 and 16 drains were randomized to the intervention and comparator, respectively. Moreover, 12 (36%) drains met the primary outcome of decontamination, 18 (55%) remained contaminated, and 3 (9%) could not be assessed. Among drains that could be assessed, 11 of 15 (74%) in the intervention group met the primary outcome of decontamination compared to 1 of 15 (7%) in the comparator group (P = .0005). Of the 11 drains in the intervention group that were decontaminated, the carbapenemase gene present at enrollment was subsequently detected in 10 (91%): 1 (10%) at day 14, 3 (30%) at month 1, 4 (40%) at month 3, 1 (10%) at month 4, and 1 (10%) at month 6. The median time to a swab yielding CPE was 1 day in the comparator group versus 14 days in the intervention group (Fig. 1). Overall, 24 drains (73%) had a carbapenemase gene (that was not detectable at enrollment) appear in the follow-up. Of patients identified as CPE colonized or infected during this study, none occupied rooms with these drains. Conclusions: Chemical, mechanical, and heat cleaning were superior to standard cleaning for CPE decontamination of hospital drains at 7 days, but these trends were not sustained. Such cleaning may be useful if applied repeatedly.Funding: NoneDisclosures: Allison McGeer reports funds to her institution for studies for which she is the principal investigator from Pfizer and Merck as well as consulting fees from Sanofi-Pasteur, Sunovion, GSK, Pfizer, and Cidara.

Revisiting heat treatment and surface activation of GaAs photocathodes: In situ studies using scanning tunneling microscopy and photoelectron spectroscopy

The lifetime of GaAs photocathodes in polarized electron guns is limited due to the delicate activation layer. An atomically clean and smooth GaAs surface is needed to deposit a robust activation layer, such as Cs2Te, with longer lifetime compared to traditional (Cs,O) activation. A previous experiment with Cs2Te activation on GaAs used heat cleaning temperatures around 400°C to avoid an increase in surface roughness [Bae et al., Appl. Phys. Lett. 112, 154101 (2018)]. High-temperature heat cleaning around 580°C, which results in a relatively contamination-free surface, could be one possible way to improve quantum efficiency. However, one should be cautious about surface roughness degradation during high-temperature heat cleaning. In this paper, we report results of surface roughness measurements on native, heat cleaned, and (Cs,O) activated GaAs photocathodes under vacuum. The results, measured by ultrahigh vacuum scanning tunneling microscopy, show that the surface roughness improves as the heat cleaning temperature is increased, by at least a factor of three for 580°C heat cleaning, compared to the native sample. Activation with (Cs,O) is shown to increase surface roughness by a factor of four compared to a 580°C heat cleaned sample. This confirms that high-temperature heat cleaning can be useful for depositing good quality robust activation layers on GaAs. We also report chemical analysis for each step of preparation for p-doped GaAs photocathodes using X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and ultraviolet photoelectron spectroscopy. Our results indicate that the (Cs,O) activation layer forms a sandwich structure consists of Cs and oxygen. We found no formation of any specific compound such as Cs2O or Cs11O3.

An effective evidence-based cleaning method for the safe reuse of intermittent urinary catheters: In vitro testing.

To determine a safe bactericidal cleaning method that does not damage urethral catheters used for intermittent catheterization. In some countries, single-use catheters are the norm; in others, the reuse of catheters is common depending on health insurance, personal preference, or individual concerns about the environment. However, no recent study of cleaning methods has been published to provide evidence for the safe reuse of catheters. Using advanced microbiological methods, a laboratory study of eight cleaning methods was conducted. Sections of uncoated polyvinylchloride (PVC) catheters were exposed to bacterial uropathogens in physiologically correct artificial urine media then tested with a range of heat, chemical, and mechanical cleaning methods. Analysis of culturable and viable but nonculturable (VBNC) bacteria was done and direct microscopy was used. Descriptive statistics were used to compare values. Heat treatments, although effective, resulted in catheter surface breakdown and damage. Ultrasonic cleaning and vinegar showed evidence of VBNC populations indicating the methods were bacteriostatic. Detergent and water wash followed by immersion in a commercially available 0.6% sodium hypochlorite solution and 16.5% sodium chloride (diluted Milton) gave consistent bactericidal results and no visible catheter damage. Combined mechanical and chemical treatment of a detergent and water wash followed by immersion in diluted Milton (the "Milton Method") provided consistent and effective cleaning of uncoated PVC catheters, showing bactericidal action for all uropathogens tested after repeated exposure. If found safe in clinical testing, this method could increase the reuse of catheters, reduce plastic waste in the environment, reduce cost, and increase patient choice.

Quantifying Implications of Deposit Aging from Crude Refinery Preheat Train Data

Heat exchanger fouling has been studied for some time in the petroleum industry. As understanding of fouling dynamics and mitigation methods improves, refinery fouling mitigation strategies are changing. The implications of deposit aging in refinery units have not been addressed in detail: aging refers to where the deposit undergoes physical and chemical conversion over time. In the 2009 Heat Exchanger Fouling and Cleaning conference, Wilson et al. [Ageing: Looking back and looking forward] presented a simple framework illustrating how deposit aging impacts heat exchanger thermal and hydraulic performance. This paper presents insights into deposit aging gained from analysis of refinery monitoring data. Two case studies are presented: (i) one from the Preem refinery in Sweden where stream temperature, flow and gauge pressure measurements indicated a higher deposit thermal conductivity in exchangers located in the hotter section of the preheat train. (ii) US refinery stream temperature, flow and plant cleaning log data, showing an increased resistance to cleaning when deposits are exposed to high temperature for a prolonged period. The use of deposit aging analysis to improve exchanger operation is discussed.

Application of the planar laser-induced fluorescence method to determine the temperature field ofwater droplets under intensive heating

Presented are results of experimental investigations concerned with formation of a nonstationary and essentially nonuniform temperature field of a water droplet (initial radius of 1 mm to 2 mm) under intensive heating in a flow of heated air (from 50◦C to 1000◦C). The method used for this purpose was a noncontact optical planar laser-induced fluorescence (PLIF) method. It is shown that temperature distribution in a water droplet is essentially inhomogeneous even under prolonged heating (to several tens of seconds). Reliability of the results of measurements by the noncontact PLIF method was analyzed by applying a group of fast miniature thermocouples. Restrictions of using the PLIF method for studying temperatures fields of evaporating droplets under high-temperature heating (over 800◦C) were marked out. Characteristic times of droplet existence (complete evaporation) were determined. It was analyzed how the temperature difference in a water droplet affects this parameter during heating and intensive phase transitions. It was substantiated that it is expedient to consider essentially inhomogeneous and nonstationary temperature field of a water droplet inmathematical modeling of the heat andmass transfer processes in high-temperature gas–vapor-droplet systems (corresponding, e.g., to burning or heat cleaning of liquids, firefighting, production of composite and gaseous fuels, their combustion, etc.).

Recovery of quantum efficiency in spin-polarized photocathodes by atomic hydrogen cleaning

We demonstrate a new method of cleaning superlattice (SL) photocathodes using atomic hydrogen that allows an increased number of repeat activations. GaAs/GaAsP SL photocathodes were activated with either conventional heat cleaning or atomic hydrogen cleaning. Repeated heat cleaning was found to gradually lower the quantum efficiency (QE) of the photocathodes, while a relatively constant QE was maintained over repeated atomic hydrogen cleaning. These results show that atomic hydrogen cleaning allows a greater number of photocathode cleanings without a loss of performance. Analyses of SL photocathodes indicated that the degradation resulting from heat cleaning can likely be attributed to the build-up of residual Cs compounds as well as damage to the GaAs cap layer. The present study also determined the 1/e lifetime for a GaAs/GaAsP SL photocathode to be 7 h at an initial current of 2.2 µA.

Ultrasound Pretreatment as an Useful Tool to Enhance Egg White Protein Hydrolysis: Kinetics, Reaction Model, and Thermodinamics.

The impact of ultrasound waves generated by probe-type sonicator and ultrasound cleaning bath on egg white protein susceptibility to hydrolysis by alcalase compared to both thermal pretreatment and conventional enzymatic hydrolysis was quantitatively investigated. A series of hydrolytic reactions was carried out in a stirred tank reactor at different substrate concentrations, enzyme concentrations, and temperatures using untreated, and pretreated egg white proteins (EWPs). The kinetic model based on substrate inhibition and second-order enzyme deactivation successfully predicts the experimental behavior providing an effective tool for comparison and optimization. The ultrasound pretreatments appear to greatly improve the enzymatic hydrolysis of EWPs under different conditions when compare to other methods. The apparent reaction rate constants for proteolysis (k2 ) are 0.009, 0.011, 0.053, and 0.045 min-1 for untreated EWPs, and those pretreated with heat, probe-type sonicator, and ultrasound cleaning bath technologies, respectively. The ultrasound pretreatment also decreases hydrolysis activation (Ea ) and enzyme deactivation (Ed ) energy, enthalpy (ΔH), and entropy (ΔS) of activation and for the probe-type sonication this decrease is 61.7%, 61.6%, 63.6%, and 32.2%, respectively, but ultrasound has little change in Gibbs free energy value in the temperature range of 318 to 338 K. The content of sulfhydryl groups and ζ potential show a significant increase (P < 0.05) for both applied ultrasound pretreatments and the reduction of particle size distribution are achieved, providing some evidence that the ultrasound causes EWP structural changes affecting the proteolysis rate.

Study on Bimetal Compound Casting Technology of Hammers

For the characteristics of the hammer handle is under bending stress and impact constantly alternating and the the main of the hammer is Withstand strong impact and friction in use，the paper designed a new type of composite casting process of hammerhead. It has two wear block imbedding in the below of the hammer ，and it set in on both sides of the axis of the hummer wiche with Inverted trapezoidal dovetail structure. The wear block was cast by high chromium cast iron, and it is properly heat treatment and surface cleaning before casting, but Into the mold after re-heated to temperature above 600 °C，At the same time，poured into the cast high-manganese steel quickly，so the block and hammer handle fused together，the block of composite hammer does not wear off in the use, and the wear resistance of the hummer improved significantly.

In-situ multi-information measurement system for preparing gallium nitride photocathode

We introduce the first domestic in-situ multi-information measurement system for a gallium nitride (GaN) photocathode. This system can successfully fulfill heat cleaning and activation for GaN in an ultrahigh vacuum environment and produce a GaN photocathode with a negative electron affinity (NEA) status. Information including the heat cleaning temperature, vacuum degree, photocurrent, electric current of cesium source, oxygen source, and the most important information about the spectral response, or equivalently, the quantum efficiency (QE) can be obtained during preparation. The preparation of a GaN photocathode with this system indicates that the optimal heating temperature in a vacuum is about 700 °C. We also develop a method of quickly evaluating the atomically clean surface with the vacuum degree versus wavelength curve to prevent possible secondary contamination when the atomic level cleaning surface is tested with X-ray photoelectron spectroscopy. The photocurrent shows a quick enhancement when the current ratio between the cesium source and oxygen source is 1.025. The spectral response of the GaN photocathode is flat in a wavelength range from 240 nm to 365 nm, and an abrupt decline is observed at 365 nm, which demonstrates that with the in-situ multi-information measurement system the NEA GaN photocathode can be successfully prepared.

A SOFC-Based Integrated Gasification Fuel Cell Cycle With CO2 Capture

The application of solid oxide fuel cells (SOFC) in gasification-based power plants would represent a turning point in the power generation sector, allowing to considerably increase the electric efficiency of coal-fired power stations. Pollutant emissions would also be significantly reduced in integrated gasification fuel cell cycles (IGFC) considering the much lower emissions of conventional pollutants (NOx, CO, SOx, and particulate matter) typical of fuel cell-based systems. In addition, SOFC-based IGFCs appear particularly suited to applications in power plants with CO2 capture. This is evident by considering that SOFCs operate as air separators and partly oxidized fuel exiting the fuel cell does not contain nitrogen from air, such as in conventional oxyfuel processes. The aim of this paper is the thermodynamic analysis of a SOFC-based IGFC with CO2 capture. In the assessed plant, syngas produced in a high efficiency Shell gasifier is used in SOFC modules after heat recovery and cleaning. Anode exhausts, still containing combustible species, are burned with oxygen produced in the air separation unit, also used to generate the oxygen needed in the gasifier; the product gas is cooled down in a heat recovery steam generator before water condensation and CO2 compression. The plant layout is carefully designed to best exploit the heat generated in all the processes and, apart from the fuel cell exotic components, far from industrial state-of-the-art, are not included. Detailed energy and mass balances are presented for a better comprehension of the obtained results.

P‐144: Photo‐Luminescence Spectra of Doped MgO Crystals and the Effect of Heat Cleaning

AbstractPhotoluminescence (PL) spectra were recorded for doped MgO crystals, irradiated by VUV light (λ=147nm, hv=8.4eV) in vacuum at room temperature. The emission band between 200 nm and 800nm was observed. Two strong emission peaks are found, one around 330nm and one centered at about 700nm. We assume that the 330nm peak is a recombination emission peak, while the 700nm peak is supposed to be related to hole traps. The crystals were then baked in air for 1h at 150°C, 450°C and 800°C, after which the samples were studied with PL analysis. The trend is that the recombination peak around 330nm increases with baking temperature, suggesting that the heat‐cleaning treatment improves the recombination emission characteristics of doped MgO crystals.

THERMAL RECOVERY OF SORBENTS BY FILTRATION COMBUSTION

We have investigated theoretically and experimentally the process of filtration combustion with hydrocarbon desorption from a porous skeleton realized, in particular, in heat cleaning of porous media out of residues of organic impurities. Two basic configurations were considered: fixed and moving beds. The problem of the combustion wave propagation in a system with three phases—gaseous, liquid, and inert solid—has been solved analytically. The specific features of this process as compared to the conventional filtration combustion of gases have been revealed. The dependences of the basic characteristics of the waves on the content of methane in the gas mixture as well as of absorbed oil and water in a porous medium have been obtained. A comparison with the experimental data has been made. Recommendations for optimizing the operation of decontamination plants on the basis of the process considered are given.

Heat Exchanger Fouling and Cleaning in the Dihydrate Process for the Production of Phosphoric Acid

Crystallization fouling and cleaning mechanisms of calcium sulphate from phosphoric acid solution have been studied experimentally and theoretically during forced convective heat transfer. The effects of flow velocity, foulant concentration, surface and bulk temperatures on the formation of scale and its removal are investigated. Close examination of the heat transfer surface at the end of a cleaning period with a cleaning agent containing 5 wt% sulphuric acid reveals that significant deposits still remained on the surface. The remaining deposits were rippled, hard and difficult to remove chemically. After clarification of the effects of operating parameters on the deposition and cleaning processes, the results of the experiments are used to develop mechanistic models for the prediction of fouling resistances of calcium sulphate during forced convective heat transfer, and for removal of the deposits by dilute sulphuric acid solutions. The predictions of the suggested models for fouling and cleaning are compared with measured data. Deviations ranging from 7% to 12% are observed which confirm the suitability of the models.

Modeling of crude oil fouling in preheat exchangers of refinery distillation units

The aim of this paper is to propose a new model for crude oil fouling in preheat exchangers of crude distillation units. The experimental results of Australian light crude oil with the tube side surface temperature between 200 and 260 °C and fluid velocity ranged 0.25–0.4 m/s were used [Z. Saleh, R. Sheikholeslami, A.P. Watkinson, Heat exchanger fouling by a light australian crude oil, in: Heat Exchanger Fouling and Cleaning Fundamentals and Applications, Santa Fe, 2003]. The amount of activation energy depends on the surface temperature has been calculated. A new model including a term for fouling formation and a term for fouling removal due to chemical and tube wall shear stress was proposed, respectively. The main superiority of the model are independent to Pr number, thermal fouling removal and determination of β based on experimental tests. Finally using the proposed model the fouling rate of Australian light crude oil has been calculated and the threshold curves to identify fouling and no fouling formation zones have been drawn.

Recent progress at SLAC extracting high charge from highly polarized photocathodes for future-collider applications

Future colliders such as NLC and JLC will require a highly polarized macropulse with charge that is more than an order of magnitude beyond that which could be produced for the SLC. The maximum charge from the SLC uniformly doped GaAs photocathode was limited by the surface charge limit (SCL). The SCL effect can be overcome by using an extremely high ( ⩾ 10 19 cm - 3 ) surface dopant concentration. When combined with a medium dopant concentration in the majority of the active layer (to avoid depolarization), the surface concentration has been found to degrade during normal heat cleaning (1 h at 600 ∘ C ). The Be dopant as typically used in an MBE-grown superlattice cathode is especially susceptible to this effect compared to Zn or C dopant. Some relief can be found by lowering the cleaning temperature, but the long-term general solution appears to be atomic hydrogen cleaning.

Filtration Combustion in Hydrocarbon Desorption from a Porous Medium

We have investigated theoretically and experimentally the process of filtration combustion with hydrocarbon desorption from a porous skeleton realized, in particular, in heat cleaning of porous media out of residues of organic impurities. The problem on the wave of such a combustion in a system with three phases — gaseous, liquid, and inert solid — has been solved analytically. The specific features of this process as compared to the traditional process of filtration combustion of gases have been revealed. The dependences of the basic characteristics of the waves on the content of methane in the gas mixture as well as of oil and water in a porous medium have been obtained. A comparison with the experimental data has been made. Recommendations for optimizing the operation of decontamination plants on the basis of the process considered are given.

Atomic hydrogen cleaning of polarized GaAs photocathodes

Atomic hydrogen cleaning followed by heat cleaning at 450 °C was used to prepare negative-electron-affinity GaAs photocathodes. When hydrogen ions were eliminated, quantum efficiencies of 15% were obtained for bulk GaAs cathodes, higher than the results obtained using conventional 600 °C heat cleaning. The low-temperature cleaning technique was applied to thin strained GaAs cathodes used for producing highly polarized electrons. No depolarization was observed even when the optimum cleaning time of about 30 s was extended by a factor of 100.