Valmet projects help Polish CHP plants meet IED

The pulverised coal fuelled CHP units, which provide heat and power for soda ash (sodium carbonate) production, have been retrofitted in response to tightening emissions requirements under the IED, with all the units included in Poland’s national transition plan. At both Inowroclaw and Janikowo projects Valmet has acted as technology provider and EPC contractor delivering the FGD systems on a full turnkey basis.

An interesting feature of the Janikowo installation is that the wet FGD system Valmet has installed there, serving two OP-140 boilers, is capable of using as reagent the product of a semi-dry FGD system already existing on the site. The semi-dry FGD system, which uses quicklime (CaO) as its principal reagent, was installed by Alstom in 2012 and treats the flue gas from three CKTI-85 boilers.

The Valmet wet FGD system, which was started up in autumn 2017, typically uses limestone (CaCO3) as the absorbent. This is itself relatively low cost, but being able to use the semi-dry FGD end-product as absorbent in the wet FGD system is essentially zero cost. The main constituent of the end product of the semi dry FGD process is CaSO3·1⁄2H2O and it typically contains around 20 to 30% of useful reagent. A further benefit is that using the material in the wet FGD avoids disposal costs that would otherwise be incurred, and avoids waste of a useful material, while reducing environmental impacts associated with disposal. In addition it can potentially achieve better SO2 removal performance than commercial limestone, as it is more reactive.

Another positive is that the end product of the wet FGD process is stable and clean gypsum (CaSO4.2H2O), useable in the building industry.

Furthermore, Valmet can point to 15 years of experience with a commercial facility in Denmark.

On the negative side are: variability of quality; and presence of large quantities of sulphites and soluble salts. There is also a need to modify some of the wet FGD process systems to accommodate the change of reagent.

But overall, operating costs are substantially reduced and the stoichiometry is such that higher sulphur coal does not entail any increase in reagent costs.

Tarja Korhonen of Valmet believes that many existing FGD systems could benefit from this “circular economy” approach. Driven by the new BREF requirements in Europe for example, there is increased interest in improved FGD performance and disposal of end products is getting more and more costly. “It would be quite feasible to retrofit existing systems to have a dual system, which allows the use of either limestone and/or waste from semi-dry FGD systems.”

At Inowroclaw, Valmet’s scope of delivery, in addition to the common wet limestone FGD system for the four pulverised coal boilers (each with a steam capacity of 110 t/h, built in the 1970s by Lentjes), includes an SCR system for NOx reduction at each boiler.

The wet FGD system was handed over in July, a record 24 months after contract signing (compared with a more typical 32-36 months). Handover of the first SCR system was in June 2016, with the last scheduled for handover in October 2018. The boilers are also being equipped with new rotating air preheaters and new flue gas fans to further extend their lifetimes.

The project represents wet FGD installation at relatively small scale (total flue gas flow, 0.5 million Nm3/h), with fuel sulphur up to 1.3%, but as expected has proved to be a very cost effective option, achieving BAT emissions levels at lowest life cycle cost.

The guarantee test SO2 level is less than 100 mg/Nm3, and that for dust less than 10 mg/Nm3.

The added benefits of combining SCR with wet FGD include ammonia slip and mercury removal, while, as illustrated by the Janikowo project, use of wet FGD opens up the future possibility of using waste lime or semi-dry FGD end product as the reagent.

Valmet ascribes the rapid implementation to “effective engineering management”, with, for example, the carrying out of building design permitting in parallel with basic engineering, and the deliberate overlapping of purchasing, execution design and site execution works.

Elsewhere in Poland, Valmet is modernising the FGD system for three coal fired boilers at PCC Rokita SA’s CHP plant.