Solval

SOLVAL: first industrial installation for industrial-scale recycling of  residues from flue gas cleaning using sodium bicarbonate

Since April 1998 Solvay has been operating on an industrial scale an original technology permitting recycling of the residual sodium chemicals from the purification of flue gases using sodium bicarbonate. With this technology, flue gas cleaning salts take on a new life as raw materials in the production of soda ash.

Originally conceived as a demonstration pilot unit, the SOLVAL unit at Rosignano (Italy), has, right from its start-up, functioned as a live industrial installation, recycling and valorizing flue gas cleaning residues from several Italian incinerators.  Today it is recognised as a reliable, competitive partner, offering an innovative service to incineration operators, in line with the Solvay Group’s Sustainable Development policy.

In simplified technical terms, SOLVAL receives from the incinerators the salts produced from the neutralisation of flue gases with sodium bicarbonate. These salts consist mainly of sodium chloride, a raw material for the production of soda ash by the Solvay process. These salts are, however, impure. SOLVAL’s precise role is to purify them by separating out all the impurities they contain. Solvay’s researchers have come up with a high performance, patented process for producing a purified brine, in total conformity with the raw materials specifications of the soda ash plant. The impurities are disposed of as final waste on an approved dumping site.

Features of the SOLVAL installation:

Location: at Rosignano, in the province of Livorno (Italy),close to the SOLVAY soda ash plant at Rosignano, to which the purified brine is piped.

Operational since:April 1998

Operator: installation operated by SOLVAL, a 100% subsidiary of SOLVAY, created for installing and operating this first demonstration unit

Processing capacity: originally designed to process 2800 t/year, the unit can currently handle over 10,000 t/year of residual sodium chemicals (sodium chloride, sodium sulphate, etc.), corresponding to the incineration of more than 500 kt/year of municipal waste.
SOLVAL processes only residual sodium chemicals from flue gas cleaning units using sodium bicarbonate in installations fitted with double filtration systems.

From laboratory idea to industrialisation: a little history lesson

The first design work on the technology applied at SOLVAL goes back to the start of the Neutrec® process in the early 1990s, when the Solvay group began tackling the challenge of large-scale purifying and recycling of residual sodium chemicals from flue gas cleaning.
Following conclusive testing in the laboratory and pilot plants, design work began in 1995 on the SOLVAL unit, intended to demonstrate the feasibility of this gas-cleaning residue purification process on an industrial scale.
The operating licence was issued in April 1998.  From then on, the Reggio Emilia incineration unit began to effectively deliver the residual chemicals and the Rosignano soda ash plant began using the SOLVAL-purified salts as raw materials. The challenge of industrialisation had been successfully met.
New clients followed, including Coriano (September 1998), Padova (1999).
In 2002 SOLVAL industrially processed over 5000 t of RSCs and is today gearing up for new growth!

A recognised contribution to environmental protection

During its brief existence, SOLVAL has already collected a number of awards:
 

• on 22 February 1999, the INCA (Consorzio Interuniversitario Chimica per l'Ambiente) prize for its technology contributing to preserving and respecting the environment.
• on 3 March 2000, a prize from the Lombardy region recognising a product which can reduce environmental pollution.
• on 3 July 2001, SOLVAL got the ‘Environment-Respecting Innovation’  prize at the “Environment 21^st Century” event at Milan, from the Italian Minister of the Environment and the President of Legambiente, Italy’s largest environmental defence association. This award honours SOLVAL’s ability to purify, recycle and convert 15,000 tonnes a year of residues from the purification of industrial flue gas into raw materials (brine).

To learn more about the process:

PROCESS - RECYCLING OF RESIDUES

Below a short guided visit of SOLVAL:

Residual Sodium Chemicals (or RSCs) are transported by truck from the incineration plant to Rosignano, where they are unloaded and placed into silos (4 silos, 2 outside and 2 inside).	Truck
Upon arrival at Rosignano, the RSCs are analyzed by the laboratory in order to control whether their composition corresponds to the SOLVAL specifications.	Laboratory
The RSCs are then dissolved in water in 2 dissolvers   (1,2 m3) with a controlled pH and with specific additives which precipitate the heavy metals. A brine is thus obtained: the salts are dissolved and the insolubles remain in suspension. The brine is collected in a buffer tank before filtration.	Dissolver
The brine is then sent to a filter-press (of 32 m3) which separates out the liquid from the solid: the liquid is now almost purified brine and the solid (filtration cake) contains all the impurities.	Filter-press Filtration cake
The filtration cake is taken out by truck and is transported to be tipped on an approved landfill site.	Truck
The brine still needs to undergo some final purification before being ready for use by the soda ash plant. It is passed through a sand filter which stops possible remaining material, and then it is passed over activated carbon in order to absorb any remaining organic components.	Sand filter, activated carbon
Final traces of heavy metal are eventually eliminated by passing over ion exchange resins: the brine is now perfectly purified and its level of purity is continuously kept under control by an analyzer.	Ion exchange resins Analyzer
The perfectly purified brine is then stocked in a tank for final control before pumping to the soda ash plant by pipeline. There it arrives in a storage tank for purified brine. The brine accounts for about 0,5% of the soda ash plants’ salt supplies.	Storage tank Pipeline
SOLVAL is also a unit which respects the environment: no aqueous effluent is produced and all the liquids, including the water used to clean the building, are collected and recycled as RSC dissolution water .	Storage tank for purified brine
To summarize, the picture besides shows some specimen of different products (from left to right): the raw residues from the incineration plant, the mixture of solid and liquid resulting from the dissolution, the purified brine sent to the soda ash plant, and the filtration cake (ultimate residues)