High efficient recovery by using bicarbonate process
Recovery of energy from waste combustion allows the reduction of the weight and the volume of the waste while reducing green house gases emission. The emission of pollutants is strictly controlled with the most stringent limit values. The SOLVAir® bicarbonate process not only enables to easily reach these limits but also minimizes the quantity of reagents needed, enhances the energy recovery, limits the amount of residues produced, and allows the recycle of residuals with the SOLVAir® residual sodium chemicals recycling solution.
Europe produces a huge amount of waste. The efforts to reduce, reuse, and recycle, the 3 R program, has begun to show results. Nevertheless, for the remaining wastes (almost 40%), there are only two options: energy recovery and disposal. Disposal is more and more restricted, as it requires a lot of space, is a waste of the energy content and eventually releases a huge amount of gases like methane and carbon oxide that contribute to the global warming.
Waste to energy installations greatly reduce the volume of waste by more than 90%, and their weight by 70%. Another advantage is the reduction of the infectious potential coming from special waste like those produced by the activity of human and animal health. The recovered energy can either be used to produce electricity and/or as steam in district heating or in industrial sites. Producing energy in this way allows to limit the use of fossil fuels, to save natural resources and limits the emission of Green House Gases, as a part of the carbon content in the waste is renewable and there is no emission of powerful GHG like methane.
In fact, the combustion of waste transforms some noxious or hazardous components in volatile materials. The raw flue gases contains harmful substances like HCl, SOx, NOx, Heavy metals and micropollutants. To avoid any pollution the European directive 2010/75/EU (Attachment 6 - Chapter 4) has imposed a strict control in all the operations of the plants, and the emission limit values -ELV- are the most stringent of all industrials sectors.
The SOLVAir® solution: dry sorbent injection of sodium bicarbonate for flue gas cleaning
The SOLVAir® bicarbonate process, easily controls the acid pollutants, reaching if necessary emission level even lower than the fixed ELV with a very low excess of reagent and a minimum of investment. The high reactivity of sodium bicarbonate BICAR® also allows an enhanced control of pollutant peaks, characteristic for waste combustion.
This very simple process consists of pneumatically injecting the ground sodium bicarbonate into the flue gas duct. Sodium bicarbonate reacts directly with the acids like HCl, SOx, HF, transforming them in the corresponding solid salts which are collected on a bag filter. The reactions form also water and carbon dioxide in a way that the weight of the residuals produced is reduced. In fact, the weight of the residuals is on average 30% lower than the weight of the sodium bicarbonate injected. For the control of heavy metals and micro-pollutants, the sodium bicarbonate shows some abatement, but in order to reach the very low level required by the Europeans Directives, a specific adsorbent is injected together with the sodium bicarbonate.
NOx reduction is accomplished by means of either Selective Catalytic Reduction (SCR) or Non Catalytic (SNCR) systems. The SOLVAir® bicarbonate Solution is compatible with both.
The SCR system uses ammonia and a catalyst to convert the NOx to N2. It needs to operate at quite high temperature in order to avoid the condensation and deposit on the catalyst layer of ammonium (bi)sulfates.
When the catalyst system is installed at the end of the treatment (tail end), like in many waste to energy plants, using sodium bicarbonate BICAR® enhances the energy recovery. First of all, the sodium bicarbonate has the highest reactivity toward SO2, allowing a very low level of remaining pollutants, and minimizing the risk of formation of ammonium (bi)sulfates. Furthermore, the extended operating temperature range for BICAR® avoids any injection of water and the subsequent cooling of the flue gases. All these facts enable the use of the catalytic device operating at the same temperature as in the bag filter, saving the energy often used to re-heat the gases.
Another great advantage of the SOLVAir® bicarbonate process is the possibility to recycle of the flue gas residuals, which are mainly composed of soluble sodium salts. The Residual Sodium Chemicals – RSC – can be purified and recycled as a raw material in some chemical processes. The SOLVAir® RSC solution is applied in two plants in Europe: Solval® in Italy and Resolest® in France.