Zhenghua Dai

Rapid co-pyrolysis of rice straw and a bituminous coal in a high-frequency furnace and gasification of the residual char

Rapid pyrolysis of rice straw (RS) and Shenfu bituminous coal (SB) separately, and rapid co-pyrolysis of RS/SB blends (mass ratio 1:4, 1:4, and 4:1), were carried out in a high-frequency furnace which can ensure both high heating rate and satisfying contact of fuel particles. Synergies between RS and SB during rapid co-pyrolysis were investigated. Intrinsic and morphological structures of residual char from co-pyrolysis, and their effects on gasification characteristics were also studied. Synergies occurred during rapid co-pyrolysis of RS and SB (RS/SB=1:4) resulting in decreasing char yields and increasing volatile yields. Synergies also happened during gasification of the char derived from co-pyrolysis of RS and SB with mass ratio of 1:4. The increased mass ratio of RS to SB did not only weaken synergies during co-pyrolysis, but significantly reduced the gasification rates of the co-pyrolysis char compared to the calculated values. Results can help to optimize co-conversion process of biomass/coal.

Study on CO2 gasification reactivity and physical characteristics of biomass, petroleum coke and coal chars

Gasification reactivities of six different carbonaceous material chars with CO2 were determined by a Thermogravimetric Analyzer (TGA). Gasification reactivities of biomass chars are higher than those of coke and coal chars. In addition, physical structures and chemical components of these chars were systematically tested. It is found that the crystalline structure is an important factor to evaluate gasification reactivities of different chars and the crystalline structures of biomass chars are less order than those of coke and coal chars. Moreover, initial gasification rates of these chars were measured at high temperatures and with relatively large particle sizes. The method of calculating the effectiveness factor η was used to quantify the effect of pore diffusion on gasification. The results show that differences in pore diffusion effects among gasification with various chars are prominent and can be attributed to different intrinsic gasification reactivities and physical characteristics of different chars.

The largest Lyapunov exponent of chaotic dynamical system in scale space and its application

The largest Lyapunov exponent is an important invariant of detecting and characterizing chaos produced from a dynamical system. We have found analytically that the largest Lyapunov exponent of the small-scale wavelet transform modulus of a dynamical system is the same as the systems largest Lyapunov exponent, both discrete map and continuous chaotic attractor with one or two positive Lyapunov exponents. This property has been used to estimate the largest Lyapunov exponent of chaotic time series with several kinds of strong additive noise.

The dimension of chaotic dynamical system in wavelet space and its application

The present Letter investigated the correlation dimension of the wavelet transform modulus of chaotic time series arising in discrete and continuous time dynamical systems. Our results indicated that the correlation dimension of the small-scale wavelet transform modulus was the same as the systems dimension. This property has been used to estimate the correlation dimension of chaotic time series with large-scale noise.

Application of a Capacitance Solid Mass Flow Meter in a Dense Phase Pneumatic Conveying System of Pulverized Coal

Capacitance measurement is one of the available methods for measuring the solid mass flow rate in the field of gas‐solid flow. Performance of a capacitance solid mass flow meter was tested in a dense phase pneumatic conveying system of pulverized coal. Results have demonstrated that the deviations of mass flow rates in the experimental set‐up are almost within ±5% for stable flow patterns while unstable flow patterns and low conveying concentration pose great measurement deviations. On the other hand, the measurement accuracies in a vertical downward flow pipeline and a horizontal pipeline are almost identical and the both are slightly better man that in a vertical upward flow pipeline. Additionally, its performances in a pilot‐scale entrained‐flow gasification plant with dry feeding are also presented and satisfying results are achieved.

A new method to estimate the oscillating singularity exponents in locally self-similar functions

A new method (WTMMP) to estimate the oscillating singularity exponents in locally self-similar function based on wavelet transform is presented. In this method, only one scale wavelet transform modulus of two kinds of wavelet is used. We illustrate our method on signals both with only one oscillating singularity and with the superposition of several oscillating singularities.

Simultaneous optimization and heat integration of the coal-to-SNG process with a branched heat recovery steam cycle

Abstract The coal-to-SNG process is an energy-intensive process, and optimizing the heat recovery network can improve the economy and energy efficiency. This study proposes a branched, triple pressure level heat recovery steam cycle (HRSC) to recover waste heat, in which one branch is responsible for recovering the waste heat from the water gas shift (WGS) unit, and the other branch is responsible for the methanation (METH) unit. The extended Duran–Grossmann model is used to optimize two heat exchanger networks to match the branched HRSC superstructure. The temperature/pressure/flow rates of the HRSC streams and the operating temperature of the WGS and METH units are optimized. The optimal bypass ratio of the WGS unit as well as the recycle ratio and split ratio of the METH unit, are 0.506, 0.681 and 0.456, respectively. The exergy efficiency of the coal-to-SNG plant is improved by 1.28% compared with the industrial plant, which can reach 54.17%.

Modelling and energy analysis of an integrated coal gasification and pyrolysis system for synthetic natural gas

Abstract The entrained-flow coal gasification is an important and attractive technology in large scale coal-based synthetic natural gas (SNG) process. In this study, an integrated entrained-flow coal gasification and pyrolysis system is proposed and investigated. The gasifier is divided into two stages in this system: one is mainly for the gasification of char and the other is mainly for the coal pyrolysis. The integrated system is studied by using a process simulation model and compared with a coal gasification system with the radiant and convective coolers. The effects of the operating conditions on the gasification performance are studied and the optimized operating conditions are obtained. It is found that the optimized steam coal ratio of the integrated system is about 250–300 kg(steam)/t (dry coal) while the gasification temperature is 1400°C. The cold gas efficiency of 88.18% of the integrated system is higher than that of 84.14% of the gasification and radiant+conductive cooler system. The coal and O 2 consumptions are relative low in the integrated system. The performance of the integrated system is highly related to the yield of tar and CH 4 in the pyrolysis stage. The overall energy conversion efficiency of the integrated system (92.26%) is slightly lower than that of the gasification and radiant+conductive cooler system (93.39%). However, the exergy efficiency is enhanced by more than 2.2% in the integrated system. The integration of the gasification and pyrolysis can effectively recover and promote energy grade of the sensitive heat in the hot syngas.

Simultaneous heat integration and economic optimization of the coal-to-SNG process

Abstract The area of the heat recovery network has a significant impact on the economic performance of the coal-to-SNG process. This paper proposes a superstructure of the methanation unit, and the number of the methanator, recycle gas extraction position (RGEXP), as well as the operating conditions, are optimized. Simultaneous optimization and heat integration are performed along with the area targeting to weigh against the operating cost and capital cost of the coal-to-SNG process. Area cost is evaluated by assuming vertical heat transfer between cold and hot composite curves. A sequential method is used to provide initial values for the simultaneous model. Results show that Case7 (2) has the best economic performance, which has 7 methanators and recycled gas is extracted from the 2nd methanator. The total annual cost of Case7 (2) can be reduced by 10.36 MM

Performance of an entrained-flow gasification technology of pulverized coal in pilot-scale plant

·a−1, and exergy efficiency can be also improved by 0.77% compared with an industrial plant.