Good combustion practice

Schindler, P. J., and Nelson, L. P. (1989). Municipal Waste Combustion Assessment Technical Basis for Good Combustion Practice. EPA-600/8-89—063, US Environmental Protection Agency,... 

The principles of good combustion practice (GCP) in Section 3 can be restated in a manner which better relates to the mechanistic aspects of PCDD/F formation and to field operational and control regimes. Updating GCP to include catalysed heterogeneous reactions in the post-combustion zone, the following goals of GCP can be identified ... 

Relevance of Current Thinking to Good Combustion Practice. With respect to issues (1) and (2), current thinking on the mechanistic aspects of PCDD/F formation does not contradict the requirements for GCP as set out in Section 5 and by the US EPA in 1987 (see Table 1), nor does it suggest that any of these requirements are superfluous. Precursor concentrations, temperature regimes, etc., are directly impacted by operational practices which have been demonstrated in both bench-scale and full-scale tests either to reinforce or to negate the goals set out for GCP in a predictable and reproducible manner. This issue is discussed further in Section 6. 

Our analysis of PCDD/F formation mechanisms and results from parametric trials on bench, pilot and full scale plant tends to reinforce rather than supplant existing strategies for reduction and control of PCDD/F emissions. Mechanistic considerations supply an underlying rationale for the requirements of Good Combustion Practice, many components of which were formulated before the reaction pathways were elucidated in laboratory experiments. The key to the... 

Carbon Monoxide Carbon monoxide is a key intermediate in the oxidation of all hydrocarbons. In a well-adjusted combustion system, essentially all the CO is oxidized to CO2 and final emission of CO is very low indeed (a few parts per million). However, in systems which have low temperature zones (for example, where a flame impinges on a wall or a furnace load) or which are in poor adjustment (for example, an individual burner fuel-air ratio out of balance in a multiburner installation or a misdirected fuel jet which allows fuel to bypass the main flame), CO emissions can be significant. The primary method of CO control is good combustion system design and practice. 

Spontaneous combustion may develop due to the heating of coal particles and slow combustion. Toxic material may be released with the oxidation of compounds present in the waste material. Runoffs, with minimal iron pyrites content, from the tip surface, promote hazards and the acid compounds may leach into domestic water supplies. All these effects may be partly or wholly overcome with proper management of the planning and design of waste heaps and good operating practices. Moreover, encouragement of the commercial use of waste material is beneficial. 

To minimize the potential for fires, the quantity of combustible or flammable material introduced and used in each SCB during target processing is limited. Good housekeeping practices are used to control the amount of combustible and flammable materials within the HCF for all modes. 

Guidance for controlling combustible materials is provided in Chapter 5 of the SNL ES H Manual. Materials used in construction must meet criteria established to limit the combustibility, flame spread and smoke generation potential of the materials. Minimization of combustible materials is also achieved by good housekeeping practices to reduce unnecessary items and lower the overall fire load. Periodic assessments, which work in conjunction with housekeeping, are conducted to identify any materials or hazards that need to be removed. 

Nitrile elastomers and PVC are considered to be harmless when used with good safety practices under normal operating conditions. Residual acrylonitrile monomers, free butadiene, and vinyl chloride monomer levels are limited and controlled by industrial and environment safety standards. Stabilization of nitrile needs to be adequate to prevent spontaneous combustion. Hazardous decomposition products include carbon monoxide, carbon dioxide, nitrogen compounds, hydrogen cyanide, hydrocarbons, vinyl chloride. 

Burning times for coal particles are obtained from integrated reaction rates. For larger particles (>100 fim) and at practical combustion temperatures, there is a good correlation between theory and experiment for char burnout. Experimental data are found to obey the Nusselt "square law" which states that the burning time varies with the square of the initial particle diameter (t ). However, for particle sizes smaller than 100 p.m, the Nusselt... 

---