THERMAL BEHAVIOUR OF A VERTICAL LUBRICATING OIL HEATING FURNACE

Abstract

The efficiency of the lubricating oil heating furnaces used for reducing the viscosity and preparing for new processes depends to a great extent on their design.In order to compute the efficiency of these furnaces, a study of the combustion process and the rate of heat transfer from the combustion gases to the furnace walls is necessary. Experiments on a geometrically similar model enables this study.

In the present work, the model scale l :10 of one full-scale furnace installed at Alexandria Petroleum Company in a battery of four such furnaces is constructed. Experiments are carried out to study the combustion aerodynamics, the heat flux distribution along the furnace model as well as the rate of heat transfer. Also, both the average total heat transfer coefficients of the combustion gases were estimated in this investigation.

Using the principles of geometrical, thermal and dynamic similarity, the results obtained on the furnace model are estimated to the full-scale furnace and consequently the thermal efficiency is computed.

The furnace model is fired by natural gas injected from a circular multi-nozzle burner header. This model is divided into six water-cooled segments; five of them represent the radiation zone while the sixth one forms the convection zone.

The experimental study of this research is divided into two parts; the first part is concerned with preliminary experiments on the circular multi-nozzle burner header with cold model using air jet and with hot model firing Butane gas. The test rig is located at the still atmosphere. The experiments of this part were carried out to study the flame characteristics such as flame length, flame cone angle and the mean burning velocity. Empirical formulas for calculating the flame length and the flame cone angle are estimated.

The second part of the experimental study was done on the furnace model with multi-nozzle burner header to study the performance characteristics of this furnace. These characteristics include the flame aerodynamics, the total heat transfer rate, the distribution of the combustion gases temperature along the furnace and the total heat flux distribution on the furnace walls. The average overall total heat transfer coefficient of the combustion gases and the average overall resultant gas temperature were calculated to help in selecting the optimum thickness of the furnace walls insulation. •

The measurements taken on the furnace model to fulfill the target of this study were gases temperature, the surface wall temperature for each segment along the furnace, the mass flow mte of the air admitted for combustion, the mass flow mte of injected natural gas, the injection pressure of natural gas, the mass flow mte of the cooling water to each segment, the water inlet and outlet temperatures to and from each segment. The total heat transfer to the walls of each segment of the furnace model is calculated.