WASTE HANDLING: Liquid wastes can normally be run thru tankage to even out flow and composition swings. Some liquid wastes must be hot in order to flow, so heat tracing and insulation design are critical. Solids in liquid wastes can deposit on injection equipment, causing plugging or poor distribution inside the burner. Vapor wastes must flow directly to the incinerator, so variations have to be accommodated quickly by the burner and instrument system.
Waste Stream Isolation: Many incinerators have to handle multiple waste streams. Mixing several vapor streams or several liquid streams for movement from the source to the incinerator can save money, but if mixing causes reactions and deposits, the cost savings are soon forgotten. Prematurely mixing a gaseous waste high in oxygen with one high in hydrocarbons can create a highly combustible mixture, and should be avoided if possible! Keeping these streams isolated until injected into the incinerator is always preferable. Where these problems are not present, it may still make sense to avoid premature mixing, since differing stream characteristics often dictate specific injection points in the burner or furnace - loss of one of the streams changes the combined waste stream characteristics and may cause burner stability problems.
Source of problem: Premature mixing of waste streams.
Flame Arrestor Plugging: Waste gases with the potential to be in the combustible range are normally run though a flame arrestor (or detonation arrestor) just prior to incinerator entry. Some waste gases can be saturated with a heavy compound such as tar. Cooling in the waste gas duct can create droplets of tar, plugging most types of flame arrestor. Some wastes contain ash or other particulate matter, creating similar plugging problems. Usually duct heat tracing, ash filtering or selection of a packed bed or other type of arrestor more resistant to fouling will solve the problem.
Source of problem: Contaminants within a vapor waste and improper flame arrestor selection.
Flash-back Protection: Sometimes a waste gas stream will pass through the combustible range in the course of plant operations. The incinerator is an ignition source. Once started, a flame proceeds at specific velocities through a combustible mixture until it is cooled below ignition temperature or passes into a noncombustible zone. Flash-back from the incinerator to the source is a common safety hazard. Methods to prevent flash-back are (1) dilution with air or inert gas, (2) enrichment with fuel gas, (3) maintenance of gas velocity above the flame velocity, (4) cooling the traveling flame using a commercial flame arrestor or (5) breaking the continuity of the combustible mixture (typically by bubbling it through a water bath). Flashback can still occur if these measures are applied improperly.
Source of problem: Waste gas enters the combustible range and proper safety hardware and logic is not present.