Animal meal

In today’s highly charged political climate, obtaining the legally required regional operating permits to dispose of animal meal (a socially sensitive subject) by incineration (an equally socially sensitive subject) requires irreproachable arguments.   In this context,  the dry treatment of flue gases with sodium bicarbonate, the only product able to meet the very stringent regulations, represents a key advantage to incinerator operators, and is proving increasingly successful.

The context:

In  France in particular, the elimination of animal meals has become a matter of critical concern. Every year, the public carcass disposal service produces 300,000 tonnes of meal from high risk animals, which is today eliminated. Since the decree of 14 November 2000, 600,000 or so tonnes a year of meal from low risk matter have been withdrawn from the animal feedingstuff chain and stored pending destruction.  Today there is an estimated backlog of 600,000 tonnes.

Right now, with France’s cement works providing one third of the destruction capacity, the Interministerial Mission for the Elimination of Animal Meal (MIEFA) is studying other processing avenues. Of the 40 projects received following the spring 2001 call for proposals, 24 involve incineration.

Thermal treatment

Broadly speaking, thermal processing treatment needs to be able:

• to destroy either the meal, or the raw waste, or a mixture of meal and raw waste, the latter solution being preferred;
• to guarantee continuous processing by the systematic presence of a back-up furnace;
• to manage the constraints imposed by the chemical composition of the meal and the raw waste, including the formation of sticky ash owing to the presence of Na and K and the weakening of the fire bricks owing to the phosphorous content and high flammability of the meals;
• to bring the combustion gases, following the final injection of combustion air, to a temperature of 850°C for two seconds;
• to make good use of the energy produced (steam, electricity or co-generation).

Flue gas treatment

As all this falls into the area of waste incineration, the gaseous emissions need to respect the emission limits set by European directive 2000/76/EC of December 2000.

For achieving this, a dry system with:

• injection of sodium bicarbonate to neutralise acid pollutants (containing high concentrations of SO₂ and, to a lesser extent, HCl),
• injection of active carbon or lignite coke to adsorb heavy metals and dioxins,
• and a deNox system for eliminating the Nox,

provides a perfect response to the requirements. Sodium bicarbonate’s effectiveness in removing SO₂ in particular is one of the keys to its success.

Fly ash from initial filtering prior to the injection of the sodium bicarbonate is apparently eligible for elimination on a category 2 dump site. Detailed research and testing are under way to examine the potential of this fly ash as a replacement construction and road building material.