Questions about the NEUTREC® process

• About the flue gas cleaning...
• About the recycling of RSCs...
• About SOLVAY'S role...
• About NEUTREC® in a sustainable development perspective

 About the flue gas cleaning...

The latest European directive on incineration imposes plants severe limits on their emissions. Is it easy to comply with these limits when using a simple system based on the injection of dry sodium bicarbonate?

YES. These extremely severe emission limits in a certain sense confer a series of advantages to sodium bicarbonate. As a matter of fact, thanks to its very high efficiency it is possible to abate a great amount of polluting acids, and obtain even much better results than imposed by the directive. So numerous household waste incineration plants are deciding to optimize their flue gas cleaning treatment, and thanks to the Neutrec process, today their HCl and SO2 emission levels are extremely reduced; the positive results of the analyses on flue gas cleaning are constantly reported to the authorities. Plants using other processes have often turned to sodium bicarbonate use to be able to comply with regulations and to resolve apparently insurmountable problems.   Since the system is based on the injection of dry sodium bicarbonate, the regulations on flue gas temperature and sodium bicarbonate dosage are not so strict; it is therefore possible to optimize temperature as well as dosage without having the one influencing the other.

Will new investments be needed if emission limits become more stringent ?

NO. The effectiveness of the sodium bicarbonate and of the NEUTREC^® process in eliminating the acids in flue gases (both HCl and SO ₂) is such that adapting to more stringent emission limits implies simply increasing the amount of sodium bicarbonate injected, in proportions which do not generally require any change in the equipment.

real life example of such adaptability

Is it true that the system based on the dry injection of sodium bicarbonate demands for a relatively high temperature (more than 160°C)? If so, does the idea not arise to attempt to regain as much energy as possible in the incinerator?

NO. First of all, the ideal temperature reached during flue gas cleaning is determined not only by the reagent that is being used. For instance, temperatures between 180 and 200°C are recommended not only to avoid problems such as condensation of the acids, but also to optimize the installation’s global energetic yield    (as in the case of the catalytic DENOX system); detailed thermodynamic calculations demonstrate that lower temperatures make energetic savings more difficult and less efficient.

Besides, the use of a reagent  implies that the array of temperatures guaranteeing the efficiency of sodium bicarbonate ranges between 140 °C and 300 °C, and even more in certain conditions.

When should additional activated carbon be injected, and does this limit the operating conditions ?

Activated carbon is used in order to meet the emission limits for heavy metals and dioxins/furans in the flue gas.

The ground sodium bicarbonate is an effective adsorbent thanks to the thermal activation phenomenon.    Where the emission limits are very stringent, activated carbon (or lignite coke) is injected simultaneously with the sodium bicarbonate, in order for example to achieve conformity with Directive 2000/76/EC concerning the incineration of waste. Certain activated carbon or lignite coke suppliers guarantee uptake performances for their sorbents when injected simultaneously with the sodium bicarbonate. The activated carbon and the lignite coke permit the levels of removal performances required by the most stringent emission limits for all flue gas temperatures under 200 °C At higher temperatures, mercury is too volatile and cannot be effectively adsorbed.

Does the NEUTREC^® flue gas cleaning process make it possible to meet the latest emission limits for dioxins and furans?

YES. As indicated above, ground sodium bicarbonate is an effective adsorbent. In order to meet the most stringent dioxins and furans emission limit (typically 0.1 ng TE/Nm³), all that is required is to inject activated carbon (or lignite coke) together with the sodium bicarbonate. This adsorbent is separated from the flue gas in the bag filter, which also captures the Residual Sodium Chemicals; the observed emission values can then be much lower than the limits mentioned above.

The only equipment required for removing dioxins is a system for storing, dosing and injecting the sorbent. Apart from this, no additional equipment is needed.

Don't the flue gas cleaning residues have to be recirculated in the cleaning system, in order to exhaust the unconsumed reagent ?

NO. The finely ground and thermally activated sodium bicarbonate presents a very high specific surface, giving it a very large removal functionality. By optimising the operating conditions, in particular by adapting the bag filter cleaning and by controlling the sodium bicarbonate flowrate, a level of cleaning is achieved which matches the strictest emission limits, with stoichiometric ratios of under 1.25. In these conditions, recirculation is not profitable, and it is preferable to avoid the ensuing complications.

About the recycling of RSCs...

Are RSCs already recycled in the chemical industry ?

YES. Purified RSCs are already industrially recycled. Just two examples:

• in the case of municipal and hospital waste incineration, SOLVAY has developed and industrialised a Residual Sodium Chemicals purification process. The industrial SOLVAL unit is in operation at the SOLVAY site at Rosignano in Italy. The RSCs of about ten incineration plants are treated in it, and the purified brine is recycled as a raw material in the Rosignano soda ash plant. The exploitation permit of SOLVAL is now extended to 15,000 t/year (representing 1,200 kt of incinerated municipal solid waste).
• the RESOLEST plant, operated in joint-venture between SOLVAY and SITA FD, realizes the same operation in France, in Rosières-aux-Salines, and the purified salts are reused in the Soda Ash plant of Dombasle.
• in the secondary aluminium manufacturing, the neutralisation of the hydrochloric acid produces RSCs consisting mainly of sodium chloride. These can be recycled in the bath of melted salts, in place of the salt which is normally consumed by this process. In this way the operator consumes few raw materials, and no flue gas cleaning residue has to be disposed of. Several installations function in this way in France and in Italy.

About SOLVAY'S role...

Does SOLVAY design or sell NEUTREC^® flue gas cleaning installations ?

SOLVAY is a chemical company and does not undertake engineering. It is the engineering companies or the customers themselves that design and build the installations. SOLVAY, on the other hand:

• makes its know-how about the process available to all interested engineering companies.
• can provide performance guarantees relating to the reagent.
• supplies the sodium bicarbonate needed for flue gas cleaning.

SOLVAY can also offer on-site services, and study the possibilities of recycling the residues.

SOLVAY support services

Where can one find the know-how for designing and building NEUTREC^® flue gas cleaning installations?

SOLVAY has the know-how relating to the NEUTREC^® flue gas cleaning process and makes it available to all interested engineering companies.

Right now, most of the engineering companies present on the market have already proposed and/or carried out NEUTREC^® installations in Europe. Any contracting authority can therefore call on the engineering company of its choice to design and/or build its installation.

Where are Residual Sodium Chemicals purified for recycling, and by whom ?

Apart from the case of 'direct recycling', the purification of RSCs with a view to recycling must in general be carried out in sufficiently large units in order to benefit from the effect of scale. This is particularly true for the RSCs from the municipal solid waste incineration, to be purified and recycled in the production of sodium carbonate. The industrial units SOLVAL and RESOLEST  are two examples.
In most cases RSC purification platforms are designed in partnership with waste professionals.

ABOUT NEUTREC® IN A  SUSTAINABLE DEVELOPMENT PERSPECTIVE

Is  the  NEUTREC®  process sustainable for  the user ?

YES.

NEUTREC® is recognized as a most efficient  process for flue gas cleaning and air quality protection,  characterized by a minimum reagent consumption and minimum  production of waste. It uses a non dangerous reagent, sodium bicarbonate BICAR®, a product that has a wide portfolio of applications in a continuously growing market (including personal care, foodstuffs and animal feed) and that is produced according the Best Available Techniques (BAT) for the protection of the environment.  

NEUTREC®  

• is very efficient in air quality protection by an optimal acid gas abatement
• does not produce liquid effluents because it is a dry process
• generates a comparatively small amount of solid residues
• solid residues can be purified and recycled.
• is described among the 'Best Available Technique' for waste incineration

Sodium bicarbonate BICAR®

• is an easy to handle reagent, harmless for the personnel
• has a low risk profile both in a safety, health and environmental perspective

In addition, BICAR®

• is a Solvay’s flagship product since more than 140 years
• is produced in multiple production plants, which assure permanent and everlasting product availability
• is used in various fields of application, from the industry to the domestic area (animal feed, personal care/pharmaceutical, flue gas cleaning, baking/foodstuffs, detergent/cleaning agents, fire extinguishers, textile/leather ) , and NEUTREC® is an application which is intrinsically devoted to flue gas cleaning and the reduction of air emissions from combustions processes.    

What about NEUTREC® process and CO₂ emissions to the atmosphere ?

NEUTREC does not increase noticeably the user’s CO₂ emission.

The use of sodium bicarbonate BICAR® in the NEUTREC® process releases CO₂ in very small quantities (about 1%), when compared to the CO₂ “naturally” present in the flue gas.

When sodium bicarbonate is injected in hot flue gas and reacts with acid gases, there is a release of CO₂ according e.g. to the global reaction

NaHCO₃ + HCl > NaCl + H₂O + CO₂

The following remarks must be taken into account :

• the emission of CO₂ by sodium bicarbonate decomposition has the positive effect that it reduces the mass of the reaction products, which are collected at the bag filter and have to be managed.
• sodium bicarbonate BICAR® production is consuming CO₂. If the global balance (from production of reagent to flue gas cleaning use) is made in comparison with the use of lime for flue gas cleaning, the CO₂ emissions are very similar (higher or lower from case to case) at equivalent levels of acid abatement rate

(extra information)

Sodium bicarbonate BICAR® production is integrated with the soda ash production  process. It uses mainly two raw materials : soda ash  and CO₂. Therefore this production does not add CO₂ emissions but to the contrary, it consumes an excess of CO₂ gas that would be otherwise discharged to the atmosphere. 

It is worth noting here that CO2 is a raw material in the soda ash manufacturing process; therefore much of the CO2 produced in a soda ash plant is internally used and not released For example, the kilns which produce lime in a soda ash plant are designed not only to produce lime (used in the distillation part of the soda ash process), but also a highly concentrated CO₂ gas to produce soda ash and bicarbonate in the carbonation units. They should not be confused with “lime kilns” used for lime manufacturing, which release all the CO₂ from the thermal decomposition of limestone in the atmosphere.

In the optimal conditions recognized in the BREF document from the EU for soda ash plants, (European Commission - BREF LVIC-s – Best Available Techniques for Large Volume Inorganic Chemicals – Solids and Others – Industry – Chapter 2 Soda Ash - October 2006)  the combination of soda ash and bicarbonate production in one plant, the global process CO₂ emissions are virtually zero (energetic needs excluded). All productions units of sodium bicarbonate of Solvay use this combination.  

What about effluents with regard to BICAR® and NEUTREC® ?

NEUTREC® process is a dry process and does not have any liquid effluents. BICAR®  itself is a dry material which generates a dry by-product, common salt.

Remarks :

• Sodium bicarbonate production process is linked to the soda ash production process and has no specific liquid effluents. Therefore an increased production of sodium bicarbonate production from soda ash does not influence the quantity and quality of liquid effluents.
• Soda ash production process has liquid effluents.  All Solvay plants are compliant to the BAT (Best Available Techniques) adopted by the European Commission for the soda ash production. The liquid effluents releases are regulated, continuously monitored and controlled, and have no harmful impact on the environment.

What is the  IPPC directive and what are exactly  BAT and BREF?

The IPPC directive (Integrated Pollution Prevention and Control) from the European Union has the aim to guarantee that all concerned industries control, limit and improve their impact on environment. To achieve this, European experts (from European Commission, Member States, Accession Countries, Environmental Associations, Industry and Industrial Associations) have set up Best Available Techniques (BAT) for the protection of the Environment as a whole which describe the best way to produce a chemical within economically affordable conditions.

From these BATs the so-called and more specific BREF (Bat REFerence ) documents have been derived  for many industrial processes, including soda ash, sodium bicarbonate, lime or waste incineration. A plant manufacturing products and operating according to its BAT (i.e. have emission limits in their permit in accordance the BAT emission levels) is therefore objectively recognized as being environmentally sustainable.

What about NEUTREC® with regard to BAT and BREF ?

The dry sodium NEUTREC®bicarbonate process is described in various BREF documents.

For example, the chapter 5 of the BREF document for waste incineration contains a table comparing the various flue gas cleaning BAT’s and it includes a column for dry sodium bicarbonate system.

Use the following link to download the BREF document for waste incineration (see position 28) http://www.jrc.es/pub/english.cgi/0/733169

What about BICAR® production with regard to its BAT and BREF ?

The BAT reference document for soda ash and sodium bicarbonate (BREF LVIC-S) is very recent (published in October 2006). It includes 13 conclusions. It is recommended to combine sodium bicarbonate production with soda ash production because of the achievable degree of integration of the two processes and the associated minimization of emissions (e.g. CO2). Emissions levels for all pollutants (incl. chlorides, ammonia, solids) and reduction measures are covered by this document. All soda ash and sodium bicarbonate production plants of SOLVAY are compliant with this BAT.

What about the liquid effluents of sodium bicarbonate  production process and their impact on the environment ?

Sodium bicarbonate production process is characterized by a high level of liquid recycling. If the plant is combined with the soda ash plant, which is always the case for the production units of SOLVAY, the bicarbonate process has no liquid waste water process stream.

Liquid effluents from the soda ash plant itself include chlorides, suspended solids, ammonia, etc… All emissions of Solvay soda ash plants are compliant to the corresponding BAT   [1].

Chlorides, for instance, are in the form of dissolved calcium chloride at low concentration in wastewater, released to sea or river according to plant location. Calcium chloride is one of the most commonly encountered chlorides in nature besides sodium and potassium chlorides and is not harmful at low concentrations. Chlorides are subject to emission limit values to ensure that chloride emissions are in line with BAT and, in case of discharge to river, that the quality objective for the river (maximum acceptable concentration)  is achieved. This maximum acceptable concentration varies and depends on the other chloride emission sources along the river, natural concentration in the water body, etc.. 

Don't hesitate to contact us for additional information.