Numerical Simulation Of Bituminous Coal And Petroleum Coke Entrained Flow Gasification And Batch Slag-Discharge System

The current study is motivated by a desire to investigate carbon containing feedstock adaptability of the entrained flow gasification, and optimize the design and operating parameters of gasification plant for its stability and reliability. The gasification performance of the bituminous coal and petroleum coke in the Opposed Multi-Burner(OMB) gasifier have been investigated by the numerical simulation method. Additionally, the flow and heat transfer between solid and liquid in a batch slag-discharge system have been studied.1. A comprehensive 3-dimensional numerical model for simulating the entrained flow gasification is developed, and the char reactivity data is extrapolated to industrial gasifier conditions by the effectiveness factor method. Comparing with industrial measured data, the simulation results show good agreements. The Nu number and Sh number of represented particles are investigated, which imply the heat and mass transfer between gas-solid phases are intensified in the impinging flow region, besides in the impinging flow region the gas velocity reduces and particle residence time increases. The above two factors favor higher carbon conversion. As increasing the oxygen-coal ratio of 0.01Nm3/kg dry coal, the gasifier temperature increases 25～30℃, the carbon conversion slightly increases and the oxygen and coal consumptions increase. When the slurry concentration increases from 59wt% to 62wt%, the gasifier temperature and carbon conversion slightly decrease, while the feedstock consumption decreases. Comparing the effects of different gasifier structure on the gasification performance, the results show the average residence time of particles in the OMB gasifier is 4-5s, which is longer than the single-top-burner gasifier. The large particles exit the single-top-burner gasifier directly which decreases gasification performance.2. As the particle diameter increases, the Thiele modulus increases and the effectiveness factor decreases. In the high temperature jet flow region and impinging flow region, the Thiele modulus of the char-steam reaction is greater than 6.9, and the pore diffusion has a significant effect. The Thiele modulus of the char-CO2 reaction is below 5 in the OMB gasifier, and the apparent reactivity is affected by the pore diffusion and chemical reaction. The effects of char kinetics on the Shenfu coal gasification performance are investigated. The results show (1) the activation energy and initial char surface area have a great effect, and the fragmentation of the char particles increases the gasification performance. (2) for bituminous coal, one of the activation energy of char-CO2/steam above 200kJ/mol is appropriate for the entrained flow gasification. (3) the OMB gasifier -performance of five bituminous coal are investigated, and the carbon conversion approaches to 98.1%～99.9%.3. The gasification performance of petroleum coke is investigated in the OMB gasifier. When oxygen-carbon ratio is 0.921 and slurry concentration is 62%, the predicted gasifier temperature is 1324℃and carbon conversion is 96.7%. As increasing the oxygen-carbon ratio, the carbon conversion increases while the oxygen consumption and the temperature at doom of the gasifier increase obviously. When the char reactivity is accelerated at 5times by catalyst, the carbon conversion reaches 99.2%, and the feedstock consumption decreases obviously. Importantly, the temperature at doom of gasifier decreases to 1345℃, which prolongs the life of refractory wall and favors for long period availability of gasifier.4. The equilibrium model of entrained flow pulverized coal gasifier is established. Based on the model validation, the gasification performance of typical coals in China are studied and effects of ash content and adding flux on the gasification performance are investigated. The results show (1) for the coal of high heat value and low ash content such as Shenfu coal and Beisu coal, the syngas productivity is increased by raising the steam-coal ratio. For the coal of high ash content and high melting temperature such as Zhangji coal and Kaiyang coal, the operating temperature of gasifier is reduced by adding optimal content flux, accordingly, the feedstock consumptions are reduced. (2) at the constant oxygen-coal ratio and steam-coal ratio, the change of±1%ash content leads to±15℃fluctuations of gasifier temperature.5. A 3-dimensional unsteady model is established to investigate flow and heat transfer between solid and liquid in the two type industrial batch slag-discharge systems, and the predictions agree well with the operation data. For the single hopper system, with increasing 1t/h of the inlet slag flow rate, the temperature of lock hopper increases 1.4℃, and the change of circulating water flow rate about 4m3/h leads to 2.5-3℃temperature fluctuations. For an introduction gasification technology slag-discharge system, when the inlet flow rate of cooling water is below 30t/h, the second lock hopper temperature is above 100℃, and the slag-discharge operation is unsafe. When the inlet flow rate of cooling water is 46t/h, the circulating water temperature is 74℃. While the cooling water at the bottom of the second lock hopper has an impact on the slag deposition, which leads to 31.8% of total inlet slag flow rate in the black water and increases the burden of the subsequent slag water cleaning system. Therefore, the introduction slag-discharge system is unreasonable on design.