China
Africa
Explore chapters and articles related to this topic
Aspects of mixed and condensed phase combustion
Published in J. F. Griffiths, J. A. Barnard, Flame and Combustion, 2019
J. F. Griffiths, J. A. Barnard
Pulverised fuel burners suffer from certain disadvantages, the most important being that in order to obtain high heat release rates the mixtures of fuel and air have to be passed in rapidly so that, for complete burning, large combustion chambers are required if the above criteria are to be satisfied. In addition, the ash tends to remain in the gas stream and can cause choking of exhaust flues. In a cyclone furnace, the combustible mixture is injected tangentially at high velocity (100–150 ms−1). The burning particles are thrown outwards by centrifugal forces and adhere to the molten slag on the walls. Although the throughput of air is very high, the residence time of the solid is extended in this way so that combustion may go to completion. The slag can be tapped off the walls. The relative motion between gas and solid ensures efficient mixing.
Advanced Fossil Fuel Power Systems
Published in D. Yogi Goswami, Frank Kreith, Energy Conversion, 2017
Cyclone furnaces were developed to burn coals that are difficult to burn in conventional furnaces. It is a form of slagging combustion technology. Crushed (not pulverized) coal along with primary air enters the cyclone and the flow transitions into a vortex via tangential injection of secondary air. This results in higher heat release and higher combustion zone temperatures. About 85% of the coal ash is removed in molten form in a single pass (no ash recirculation) [36]. High combustion temperature is the reason for one major drawback of the cyclone furnace: high NOx emissions. Air-staging, reburning, and post-combustion treatment (e.g., SCR) provides varying degrees of NOx control capability.
By-Product Utilization
Published in B. K. Bala, Agro-Product Processing Technology, 2020
A cyclone furnace may be horizontal or vertical. A horizontal cyclone furnace consists of a slightly inclined cylinder, lined with firebricks, into which air is ejected tangentially at a very high speed. Figure 8.1 shows a schematic representation of a horizontal cyclone furnace. The fuel introduced at one end is entrained by the revolving mass and is thrown against the cyclone walls where it intimately mixes with air and burns. The flue gases leave through the aperture at the other end of the cyclone furnace. Cyclones are designed for positive pressure operation. Generally, cyclones require an air blower with high static pressure.
Dual-Stage Drying Process of Lignite Using Pilot Scale Coal Rotary Dryer
Published in International Journal of Coal Preparation and Utilization, 2019
Phiciato Phiciato, Dedi Yaskuri
However, the single-stage dried product is already more susceptible to spontaneous combustion than undried lignite [24] which makes dual-stage drying even more prone to oxidation attack. For this reason, we modify the configuration of flue gas flow to reduce oxygen level in rotary drum as seen in the process flow diagram in Figure 1. The idea is actually based on self-heat recuperation of fluidized bed drying where heat generated from the reactor is recirculated as pretreatment for feedstock. All the energy involved in drying can be utilized as the heat source for the subsequent drying process and thus the total energy consumption can be reduced significantly [25]. In this case, a similar technique is adapted by recirculating hot flue gas generated from cyclone furnace into intermediate chamber. Hot flue gas was recirculated from wet scrubber to intermediate chamber so that the oxygen levels in rotary drum were reduced to 16.5% as shown in Figure 5. The purpose is not to improve energy efficiency but to reduce oxygen content inside the rotary drum. Intermediate chamber has an important role in supplying oxygen-limited gas to rotary dryer, thus the operational temperature can be set higher. As the oxygen content decreases, the operator can set higher temperature to optimize moisture removal. For all MFR values, the oxygen levels tend to decline with the increase of average temperature of rotary drum. It is because the additional combustion of tangentially injected coal in cyclone furnace promotes the increase of volumetric flow rate of flue gas. The additional heat generated from combustion allows us to optimize moisture removal by increasing inner temperature of rotary drum. As the temperature of rotary drum increases and the oxygen level drops, the operator can set higher MFR.