Oxidation of lean methane in a two-chamber preheat catalytic reactor

doi:10.1016/j.ijhydene.2017.04.187

International Journal of Hydrogen Energy

Volume 42, Issue 29, 20 July 2017, Pages 18643-18648

https://doi.org/10.1016/j.ijhydene.2017.04.187 Get rights and content

Highlights

•
A novel method for mitigating lean methane was proposed.
•
The effects of the space velocity and the methane concentration were studied.
•
Lean methane abatement can be achieved by the proposed system.

Abstract

This paper presents the results of lean methane oxidation in a two-chamber preheat catalytic reactor. A preheat catalytic reactor was built, and the effects of the space velocity (3800 h⁻¹ to 8100 h⁻¹), the inlet methane concentration (0.6 vol.% to 0.8 vol.%) and the inlet temperature of catalytic oxidation bed (420 °C–540 °C) were experimentally investigated. The results showed that when the space velocity is low, the methane conversion rate maintains a high value. But when the space velocity is higher than 7100 h⁻¹, the methane conversion rate decreases dramatically. With the increases of the inlet methane concentration and the inlet temperature, the overall temperature of the oxidation bed increases rapidly, the temperature increment of the first catalytic ceramic layer increases, the methane conversion rate increases.

Introduction

Coal is the dominant energy source and coal bed gas (the main ingredient is methane) is released during the period of coal mining. In order to ensure the safety of mine operation, the coal bed gas is usually diluted in the way of gas extraction and then is released to the atmosphere, which leads to lean methane with very low methane concentration (0.2 vol.%∼0.75 vol.%). The global emission of methane from this source is estimated at roughly 40 billion Nm³. As the methane concentration is very low, the lean methane is difficult to combust with a traditional burner, which not only pollutes the environment but also wastes the energy resource. Thus, the research on the utilization technologies of lean methane is of great significance [1], [2].

The reverse-flow reactor is an effective way to utilize lean methane, including thermal flow-reverse reactors (TFRRs) and catalytic flow-reverse reactors (CFRRs). Liu [3], [4] and Mao [5] systematically studied the oxidation characteristics, the resistance characteristics, the mixing characteristics and the flow distribution of thermal flow-reverse reactors. Gosiewski [6], [7] analyzed the effects of oxidation bed temperature on oxidation and the emission characteristics of the reactors. Wang [8], [9] studied the effects of the heat loss of the device, oxidation temperature and temperature filed of hot-start on the running performance, and the effects of the methane concentration, inlet velocity, wall heat loss, switching time and porosity of ceramic honeycomb in a thermal flow-reverse is also studied. Su [10] and Yin [11] respectively studied the effects of methane concentration and the flow rate on oxidation characteristics of CFRRs. Litto [12] studied the effects of inlet velocity, geometric parameters and switching time on the performance of the device. Wang [13] studied the effects of space velocity, methane concentration and switching time on the bed temperature distribution. Jeon [14], Chen [15] and Vigneault [16]studied the catalytic combustion of methane. Fernández [17] designed a reverse flow reactor adequate to treat a typical real coal ventilation stream. In order to get higher heat recovery, the reversing device is necessary in reverse-flow reactors to change the airflow direction periodically, which leads to problems like requirements for higher reliability, periodic fluctuation of oxidation bed temperature filed, big volume and power consumption.

Zheng [18] presents a preheat catalytic reactor to combust lean methane. The reactor adopts a new working principle and different CFRRs and TFRRs, which isn't reverse-flow. A schematic diagram is shown in Fig. 1. This method brings a stable and reliable temperature field and high heat recovery efficiency with compact structure and small flow resistance. So it is very economical and feasible. The lean methane is preheated by high temperature flue gas from the reactor in the heat exchanger. The heating lean methane flows into the catalytic reactor and is catalytic combusted. The high temperature flue gas from the catalytic reactor flows into the heat exchanger to preheat fresh lean methane. In this paper, a two-chamber preheat catalytic reactor was built, the effects of the space velocity, the inlet methane concentration and the inlet temperature of catalytic oxidation bed were experimentally investigated.

Section snippets

Experimental reactor system

All experiments were carried out in a two-chamber preheat catalytic reactor. A general view of the experimental apparatus is shown in Fig. 2, while a simplified flowsheet of the apparatus is shown in Fig. 3.

The designed rated flow of this experimental system is 2000 Nm³/h. The experimental system includes five parts: the gas supply system, the preheating system, the startup system, two reaction chambers and the parameter acquisition system. The gas supply system includes a centrifugal fan, a

Temperature distribution in catalytic oxidation bed

Fig. 5 shows the average temperature distribution of the reaction chamber 1 and the reaction chamber 2 in self-heating condition for a space velocity of 6000 h⁻¹ and a methane concentration of 0.8 vol.%. The average temperature is the average value of the seven temperature measurements of a same temperature measuring layer. As is shown in Fig. 5, with the increase of X axial direction length, the average temperature increases, but the temperature raises rate decreases and the average

Conclusions

(1)
With the increase of X axial direction length, the average temperature increases, but the temperature rise rate decreases and the average temperature is stable finally. The great region of temperature rise is first catalytic ceramic layer. The average temperature distributions of the reaction chamber 1 and the reaction chamber 2 are similar.
(2)
The methane conversion rate maintains a high value when the space velocity is less than 7100 h⁻¹. When the space velocity is more than 7100 h⁻¹, the methane

Acknowledgments

This work was supported by the China National 863 High Technology Fund Project (2009AA063202), Shandong Provincial Science and Technology Development Program, China (2012GGX10417) and Shandong Provincial Natural Science Foundation, China (ZR2013EEQ005 and ZR2014EL030).

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¹: School of Transportation and Vehicle Engineering, Shandong University of Technology, Xincun Road 266#, Zibo City 255049, Shandong Province, China. Fax: +86 533 2782616.

View full text

Oxidation of lean methane in a two-chamber preheat catalytic reactor

Highlights

Abstract

Introduction

Section snippets

Experimental reactor system

Temperature distribution in catalytic oxidation bed

Conclusions

Acknowledgments

Int J Coal Geol

Chem Eng J

Chem Eng J

Fuel

Appl Energy

Catal Today

Int J Hydrogen Energy

Int J Hydrogen Energy

Int J Hydrogen Energy