CRUDE OIL FOULING ON HEAT TRANSFER SURFACES

Hydrocarbon fouling in a petroleum refinery crude preheat train has been identified as a critical issue affecting the economy of the plant very badly. Fouling undergoes different mechanisms at different stages of heating the crude oil in the preheat train. Understanding the fouling mechanisms is essential in formulating appropriate fouling mitigation strategies. The present research focuses on the study of fouling characteristics of four different Malaysian crude oils through experiments in a pilot-scale, high-pressure and high-temperature recirculation flow loop fitted with two identical fouling probes. The procedures reported in the open literature employ very high surface temperatures. It has been identified in this study that there is a maximum surface temperature/heat flux beyond which the forced convective heat transfer regime changes to boiling regime. As the industrial preheat exchangers operate at forced convective heat transfer regime, it is therefore, necessary to carry out the experiments in the same heat transfer regime. In this study, an improved method has been developed for calibrating the surface temperature using the heater temperature measurement by the Wilson plot technique. This method enables identification of the heat transfer regimes more accurately. Maximum heat flux under the forced convective heat transfer regime was determined for each crude oil at the corresponding operating conditions. A model to determine the maximum heat flux has also been proposed in terms of the crude oil true boiling point data. A series of experiments were planned and carried out to study the fouling characteristics of different crude oils at different initial surface temperatures, bulk temperatures and flow velocities at a pressure of 50 bar. Data from each experiment were collected, processed and the resistance due to fouling was determined. The induction periods and the initial fouling rates were estimated from the fouling resistance profiles. It was observed that the induction period decreased with an increase in initial surface temperature; increased with an increase in the bulk temperature and flow velocity. It was also observed that the initial fouling rates increased with increase in initial surface temperature; decreased with increase in bulk temperature and flow velocity for all the crude oils. The experimental data were analyzed using the existing threshold fouling model. This model assumes the rate of fouling is the net effect of fouling precursor formation through chemical reaction and deposition, and removal by the wall shear. The apparent activation energy values were estimated for the crude oils at different bulk temperatures and flow velocities. It was observed that the variations in the apparent activation energy values for flow velocities of 0.4 and 0.5 m/s are insignificant and that it increased linearly with increase in the bulk temperature. The existing threshold fouling models predict an increase in the initial fouling rates with an increase in the film temperatures. Although the existing models predict the fouling rates well for increase in film temperature due to increased surface temperature at constant bulk temperature, they fail to predict the fouling rates for an increase in film temperature due to the increase in bulk temperature at constant surface temperature. A new threshold fouling model was developed to account for the effect of bulk temperature on fouling by considering the apparent activation energy as a function of bulk temperature. The new threshold fouling models for the crude oils tested were proposed. The proposed threshold fouling model has been found to be in good agreement with the experimental data

A Review of Parameters and Mechanisms in Spray Cooling

Miniaturisation in avionics, electronics, and medical appliances has led to demands for rapid heat dissipation techniques. The spray cooling technique has gained importance recently due to its advantage over other cooling methods. Parameters affecting heat transfer mechanisms during spray cooling are contemplated. This review presents different heat transfer parameters and their effect on spray cooling by analysis from past studies. Heat transfer surface modifications and different coolant variations to enhance heat transfer effectiveness are also reviewed. Apart from high heat flux having more applications, low heat flux studies have also grabbed the researchers to find solutions with a temperature range lower than 250˚C. Therefore, the upcoming spray cooling technology will have broad applications that will contribute to the maximum efficiency of the heat removal rate

Production and characterization of agro-based briquettes and estimation of calorific value by regression analysis: An energy application

Biomass in the original form having low bulk density results in huge transportation & storage costs, and cannot be used as an effective combustible fuel. Densifying biomass by briquetting/pelletizing technology helps to reduce the above said problems and improves the effectiveness of biomass as combustible fuel. In the present study, briquettes were produced by using rice husk and carbonized rice husk with starch and bentonite clay as binders. The bulk density and compressive strength of briquettes produced were determined. It was observed that bulk density values of briquette samples increased with increase in binder percentage in the mixture up to 6% and decreased with further increase in binder concentration. Similar trend was also observed for compressive strength of briquettes. Proximate analysis of briquettes was evaluated as per the standard methods. A mathematical equation to estimate calorific value of biomass briquettes based on the proximate analysis of briquettes was developed by using regression analysis. It can be inferred that the predicted data from the proposed model closely match with the experimental data with a R2 value of 0.94 and root mean square deviation (RMSD) of 0.0659. Keywords: Briquettes, Regression analysis, Binder, Compressive strength, Bulk densit

Study of Extraction Kinetics of Total Polyphenols from Curry Leaves

Solid-liquid batch extraction of total polyphenol content from curry leaves (Murraya koenigii L.) was studied in this paper. The effect of different solvent concentrations and temperatures on total polyphenol content was investigated by performing batch experiments. The experimental studies showed that the kinetics of solid-liquid batch extraction was influenced by different solvent concentrations and temperatures. In solid-liquid batch extraction, more recovery of total polyphenols was obtained for 50% (v/v) aqueous methanol and at 333 K temperature. The total polyphenol obtained at optimum conditions was 79.34 mgGAE/L. Mathematical modelling is an important engineering tool used to study the kinetics of extraction as well as in the design of the extraction process to reduce time, energy, and chemical reagents. Peleg and Power law, the two mathematical models, were used to study the kinetics of the batch extraction process. The Peleg model showed the best fit to explain the kinetics of process with R2 > 0.99. Further conventional extraction methods are compared with the novel extraction method

Briquetting of Dry Sugarcane Leaves by Using Press Mud, Cow Dung, and Buffalo Dung as Binders

The world’s population is increasing rapidly. This means that energy consumption and demand for energy are also increasing at the same rate. It is estimated that energy will need to be provided to 9 to 10 billion people by 2040. India is a leading consumer of energy in the world. In particular, it consumes a large amount of oil and natural gas to fulfil its energy demand. Due to uncertainty in the supply of oil and natural gas and their prices as well as environmental pollution, there is a need to shift towards other energy sources. Biomass is one of the first energy sources with specific properties and abundant availability. Today, 10% to 14% of the world’s energy supply is provided by biomass sources. Using agricultural waste (biomass) to make briquettes to generate power can be an alternative solution to the problems related to their disposal and pollution. The present work investigates the optimum ratio of dry sugarcane leaves to binders and optimum load and selects the best binder (cow dung, buffalo dung, and press mud) for making high-quality briquettes. The physical parameters and proximate analysis of the dry sugarcane leaf briquettes with the cow dung, buffalo dung, and press mud binders are investigated. The dry sugarcane leaf briquettes with the cow dung binder have the highest gross calorific value, net calorific value, split tensile strength, tumbling resistance, shatter resistance, and energy density ratio (16262.31 kJ/kg, 15362.1 kJ/kg, 7.164 kN/m2, 87.84%, 12.75%, and 0.9296, respectively). The estimated results show that cow dung is a better binder for making high-quality dry sugarcane leaf briquettes than the buffalo dung and press mud binders