Research On Fuzzy Risk Assessment Of Urban Buried Gas Pipeline

When cast-iron pipes formerly used to transfer manufactured gas are changed todeliver natural gas, Gas-conditioning is a transitional technique in gas conversionprocess, and a approach to reduce leakage effectively. Atomization is a technique toput the humidification agents into spray and inject them into natural gas, and themain device is the humidifier. Therefore, the paper aims at the humidifier injectingspray under pressure which widely uses the power driven by a pressure differencebetween mid-pressure and low-pressure parts.The background and development about gas pressure atomization technique hasbeen summarized, and the present state of gas atomization technique and atomizationnozzle has been analyzed, determining the style of humidifier and its initial andboundary conditions, discussing the design method of atomization nozzle of thenatural gas humidifier and designing the laval nozzle, which is composed of thestraight section, the contraction section contouring with Witozinsky curve and thedivergent section contouring with cone shape. Based on the study above, sets up thegeometric model of the laval nozzle; fixes its initial and boundary conditions;analyzes the gas-liquid two phase flow (using CH4and water) of the computationalfield inner and outer the laval nozzle by numerical simulation with CFDsoftware—Fluent; improves the design scheme of laval nozzle, and propose a betterdesign; mainly designs a natural gas humidifier whose spray is good enough to meetthe requirements.The numerical simulation is conducted at the initial and boundary conditions asfollows: selects the3D implicit formulation solver, unsteady time solver, ideal-gasdensity properties, standard k-epsilon viscous model and the default under-relaxationfactors; determines the convergence by the residual and mass conservation principle.Based on the conditions above, the paper firstly employs Eulerian model to simulateand analyze the gas-liquid two phase flow of the computational field inner the lavalnozzle, and gains the flow pressure and velocity contours of humidifier with single or double-tangential-way water inlet at any position; Secondly, the paper uses DPMmodel to simulate and analyze the breakup process of liquid stream outer the lavalnozzle, gains the flow pressure and velocity contours and the droplet distribution ofdifferent performance, including gas pressure, outlet hole diameter, mass flow rate ofthe gas and so on. The results show that:(1) humidifier with double-tangential-waywater inlet could improve the uniformity effectively;(2) To make droplets smallerand improve the spray quality, pressure and mass flow rate of the gas could beincreased, outlet hole diameter or length could be reduced, and all of the factors willbe a match;(3) the paper has accomplished the development of humidifier at the firststage, and the smallest droplet diameter is1.6μ m, satisfying the basic demands ofgas atomization technique.