ATS recently commissioned first waste heat recovery system in a container glass facility

Details of the Flue Gas Treatment Plant (quencer and dry scrubber)

Established in 1938 as a handcraft plant, Vetrobalsamo S.p.A. is located on a 180.000 square meters area in Sesto San Giovanni and thanks to the ecological sustainable choices made, it is considered as a urban glassworks, very well integrated in the city area.
Specialized in the creation of customised bottles, Vetrobalsamo is able to give an answer to any kind of requirements of the customer, by manufacturing more than half a million glass bottles per day in Maya and flint colours.

Unique glassworks in the glass field in Italy to have installed oxy-fuel furnaces, Vetrobalsamo manufactures bottles with low carbon footprint, letting the customers to be on the market in conditions of absolute pre-eminence in terms of environmental sustainability. However in this site no pollution control plant was installed since ATS has been awarded by the contract at the end of 2012.

The glass manufacturing process will normally generate some specific pollutants like dust, SO2, that can be found in different quantities by considering the type of fuel normally used into the furnace burners, HCl, normally just in traces, and NOx.

The amount of SO2 released during glass manufacturing is mainly determined by the sulphur content of the fuel, the sulphur content in the batch and the sulphur absorption ability of the glass produced. The sulphur added to the batch is partly bound to the glass as SO3 or sulphite in the reduced molten glass.

As result of the presence of this pollutant, accordingly the IED, it is generally mandatory to have a sulphur neutralization before leaving the flue gas going into the atmosphere. In this particular case we provided a sodium bicarbonate injection into a Venturi dry scrubber. This particular system has several advantages:

1) By providing an injection of reagent into the Venturi throat, so in a turbolent region, we perform a very good mixing between bicarbonate and pollutants.

2) The ascending and overturning parts are realized in order to have a low ascending speed, this fact will guarantee a contact time higher then 3.5 sec that will allow the completion of the reaction before reaching the filtration device.

As results of those points we were able to provide a system that can reach abatment of SO2 in the order of 90% with a stoichiometrical ratio of just 1.15.

As last stage it has been also provided an high efficiency fabric filter (protected by a cooling tower just used during maintenance periods of the waste heat recovery boiler), in order to collect all the dust coming from the glass furnace as well as all the reaction product between bicarbonate and acid pollutants, able to provide under design condition a captation yield that exceed the 99.9%.

Then due to a contract signed with local authorities, we received also the request for a Waste Heat Recovery System (WHRS) that should be able to recover the thermal energy of the flue gas in order to feed the local district heating, and with the surplus of energy still present in the gases produce all the possible electrical power available. In particular it was required to recover up to 5MWth coming from two furnaces and being able to produce up to 500kWe from the surplus of energy not used by the district heating.

The saturated steam generator, for the waste heat recovery, has been designed in order to ensure a vigorous natural circulation in all the different heating loads coming from the furnaces.

Flue gases going through the steam generator will cool down from 750°C to 200°C, that is a suitable temperature both for the reaction with sodium bicarbonate and for the dust collection by a fabric filter in order to guarantee the requested emissions.

Medium pressure saturated steam (15÷24 bar(g) with a title between 80÷95 %) is expanded inside a twin screw turbine connected to a power generator with nominal production of 500 kWe. Subsequently, the saturated steam coming out from the twin screw expander at a lower pressure (0,5÷1,5 bar(g) ) exchange the residual thermal power in order to heat water for the local district heating network. This condensing heat exchanger is able to treat up to 8.000 kg/h of saturated steam at 1,5 bar(g) with an heat input of 5MWth.

In case of lack of request by the district heating network, or in case of any possible fault, a system of condensing air cooler will ensure the safety of the system. The resulting condensates will be in this way recirculated inside the boiler in order to close the loop. A demineralized water plant, with a production of 500 lt/h, will guarantee the continuous feeding of the steam generator.

Source: Air Treatment System/atsecologia.it