Development Of Pressurized Submerged Combustion Vaporization System And Their Basic Characteristics Investigation

With the growing world energy shortage and environmental impact, whichadvocates and aims for more stringent emission controls and energy saving. To solvethe increasingly energy and environmental problems and take into account thecombustion which is the basic approach of energy conversion and utilization, theproblem can be solved from two ways: increasing the proportion of clean and highefficient energy in energy consumption; organizing reasonably the combustionprocess and developing clean and high efficient combustion technology andequipment. Submerged combustion technology, as a direct contact heat transfer rule,has been widely applied in many areas, which has exactly the characteristics of highefficiency and low emissions. But heating temperature is low for conventionalsubmerged combustion, which makes its applications aimed at heating are limited. Atthe same time, exhaust gas temperature is relatively low, which is one of theadvantages of submerged combustion, but also makes the exhaust heat losses aredifficult to recycle. Clean compressed natural gas is chosen as the fuel, deepening theapplication of submerged combustion technology and broadening its scope ofapplication, on this basis some basic theories and experimental studies are carried outabout the pressurized submerged combustion (PSC) which is the secondarydevelopment of submerged combustion. The PSC technology can improve the heatingwater temperature, and may be appropriate to increase the exhaust pressure andtemperature. According to enhance the different ranges, it can be applied to oil andgas field produced water treatment, concentration transportation of crude oil and thefuture target of heavy oil thermal recovery respectively, and which will offers a newtechnical solution for the resource utilization of oil and gas field sewage. The maincontents include:Thermal economic analysis is carried out about the pressurized submergedcombustion evaporation/vaporization (PSCE/PSCV), which indicates the subject ofexperimental research combining with the existing experimental basis. To sort out andsummarize the related theory of PSC technology and point out how to select some ofthe important thermal parameters of PSC such as the excess air coefficient, volumeheat load of the furnace, etc. The higher pressure is favorable to combustion. Throughconsidering the interaction of the two phases and the influence of pressure on the premise, gas-liquid two-phase flow of the PSC system can be studied with some of theclassical methods of single-phase fluid dynamics.Some key laboratory equipment components are designed such as the PSC burner,the evaporation, the immersion tube, etc. The PSCE test bench is set up. Thecombustion chamber pressure fluctuation characteristics of the PSCE are studied bytheoretical analysis and the cold state test as well as numerical simulation. Studieshave shown that pressure difference fluctuation assumed periodic change in the PSCV.With the increase of gas velocity and submergence depth, the fluctuating range ofpressure difference enhanced, and the influence of air flow on pressure fluctuationwas more prominent than submergence depth. Immersion tube with bubbling holescan reduce pressure fluctuations. Under the same inlet conditions, the higher backpressure is conductive to weaken the pressure fluctuations, and the pressurefluctuation of PSC chamber is mainly determined by the pressure difference in thecold state. The optimal solution consist on expanding the cross-sectional area ofbubbling tube for reducing liquid level fluctuations in the burner structure, but thiswill increase the gas pressure fluctuation in the chamber, resulting in the need todetermine an optimal compromise relation of cross-sectional area and submergencedepth as well as the diameter of the vaporizer for practical applications.Numerical simulation studies are carried out for0.5MPa and5MPa PSC burnerby Composition PDF Transport model and Eddy Dissipation (ED) model ofFinite-rate Chemistry Models respectively. Visual images and parameter values areobtained for temperature field and velocity field of the chamber as well as outlettemperature and velocity, etc. All of these numerical simulation studies guideeffectively the design of PSC burner and debugging of hot state experiments. NOxpollutant formation model is introduced when carrying out numerical simulation of5MPa PSC burner, PSC is confirmed that a low NOx combustion technology by thenumerical simulation. The impact of secondary combustion air is considered in thenumerical simulation of0.5MPa PSC burner. The numerical simulation results showthat secondary combustion air entrances are set too close to the front of the PSCburner, and resulting secondary combustion air in reducing flue gas temperature, inother words it does not play a good secondary combustion role. So the secondarycombustion air is almost not used in the actual experiments. The eddy dissipationmodel of Finite-rate Chemistry Models is used to simulate temperature field andvelocity field of the combustion chamber which is pressurized from0.5MPa to3.0 MPa and CO2and NO mass fractions along the axis are also obtained by thenumerical simulation. The numerical simulation results show that the flametemperature of the burner center axis increases with the increase of pressure. In thesame inlet mass flow conditions, the starting position of the combustion reactionmoves to the airflow upstream with the increase of pressure, that is the primary flamezone forward, and the flame surface gradually narrows.Acomparative hot state experiment study is carried out about diffusion/premixedhigher pressure nozzle in the lower back pressure. The experimental results show thatlow-pressurized submerged combustion is suitable for using premixed combustionnozzle, and high-pressurized submerged combustion is suitable for using diffusioncombustion nozzle, but it is very important for ensuring well-mixed state of fuel andcombustion air in the high-pressurize submerged combustion nozzle. There is a goodagreement theory value with experiment value of the evaporation initial temperature,and theory value with experiment value of the constant evaporation temperature isalso in good agreement. All these show that it is successful for the design of highefficient vaporizer based on PSC. Some hot state experiments of PSC are carried outfor different immersion tube nozzles, and studies show that nozzle with bubblingholes helps to reduce pressure fluctuation and enhance the heating rate of heatingwater as well as strengthen the gas-liquid heat exchanger efficiency. In particular, thecirculating pipe (airlift) with bubbling holes is the most effective, and its effect isbetter.Pollution emission experiments of PSC show that there is a small change forNOx and CO emission concentration with immersion depth. With the increase ofexcess air coefficient, NOx emissions increase first and then decrease, and there is apeak value with the extreme point of excess air coefficient is about1.3; CO emissionless than40ppm is relatively low, and its value can be zero when there is good PSCstate and back pressure is stable. NO and NOx emission concentration is less than20ppm, and the pollution emissions of the steady-state experiments are far below thenational standard, the corresponding emission measure is lower if PSC is carried outwell. Efficient vaporization based on pressurized submerged combustion exactly is akind of high effective, low emission energy-saving new equipment.Thermal efficiency experiments of PSC show that its thermal efficiency is higherthan atmospheric pressure submerged combustion. The heat loss and the total thermalefficiency of PSCV are analyzed. Analytical studies have shown that heat loss of flue gas accounting for5.55%of the combustion heat, and it is main heat loss for thePSCV; due to better wall insulation, the heat loss of wall of the PSCV, onlyaccounting0.61%of the combustion heat,which is very small share. As the entire flueis placed in the PSCV, flue radiant heat loss is negligible, which is another mainreason for the higher thermal efficiency of PSC. From certain condition, analysis andcalculation of the total thermal efficiency show that thermal efficiency of PSCV is upto96.08%. Considering secondary use of flue gas waste heat, the total thermalefficiency of low calorific value can reach101.63%.