EfW plant introduces HCl monitoring solution to reduce reagent costs and support future BREF requirements

HCl Abatement Control Solution | LAS 5000XD

Customer: EfW plant, United Kingdom

Challenge: Measure and control process HCl gas prior to abatement

Solution: LAS 5000XD in-situ analyzer

Hampshire (United Kingdom) Energy from Waste (EfW) plant is operational since December 2004. The site processes 180,000 tonnes of non-recyclable waste per annum, through two streams, to supply up to 16MW of electricity to the National Grid.

BACKGROUND

Exhaust emissions from an EfW plant contain a variety of gaseous compounds which are regulated by the Industrial Emission Directive (IED).

Two of these gaseous compounds are hydrogen chloride (HCl) & Sulphur Dioxide (SO2), both of which are acid gases. Under normal operation, both are emitted in small quantities from EfW plants.

Small quantity emissions are the result of very good abatement control technology. Lime is injected into the abatement plant, which effectively ‘scrubs’ any acidic components that are present in the gas stream.

However, due to the inhomogeneous nature of the feedstock (black bin waste) the concentration of HCl & SO2 can vary, so both need to be carefully monitored.

ISSUE FACED

The latest revision of the IED will see emissions limits reduced significantly, which is highlighted in the table below.

CURRENT LIMIT

(mg/m3) NEW LIMIT, CURRENT PLANT

(mg/m3) NEW LIMIT, NEW PLANT

(mg/m3)

HCl 10 8 6

SO2 50 40 30

With these new limits, the efficiency of the abatement control plant becomes increasingly important. Until now, site operators would estimate how much lime reagent was needed by monitoring the final emission to atmosphere. A feedscrew would then increase/decrease the amount of lime injected into the gas stream in a bid to reduce emissions.

The problem with this method is the reliance on a ‘feed-back’ technique. Site operators have been frequently adding too much lime. Overdosing is common but this comes at a cost in both emission limit breaches & lime wastage.

SOLUTION

The Hampshire EFW site turned to ENVEA for a cost-saving solution that can be adjusted to future legislative changes.

The LAS 5000XD TDL was proposed, even though it was limited to HCl measurement only. ENVEA’s knowledge of the EfW process, the known concentration of the raw gas & the ELV proved that if you control the HCl, the SO2 would be controlled as a byproduct.

The in-situ gas analyzer was trialed to measure process HCl gas prior to abatement so accurate amounts of lime could be added.

The LAS 5000XD is a precise, reliable & maintenance free solution. It measures HCl which allows the plant to run in fully automatic mode, where the lime dosing is controlled from the instrument readings.

Now, raw gas measurement can be performed by the LAS 5000XD prior to abatement to manage the feed-forward.

This solution has been largely appreciated by the plant operators because it’s the first time since the site became operational that their abatement plant has been fully automated.

EfW plant introduces HCl monitoring solution to reduce reagent costs and support future BREF requirements

CUSTOMER BENEFITS

Allows the abatement plant to operate fully automated without intervention thus removing guesswork and improving accuracy.

Meets current Emission Limit Values (ELVs) and supports future BREF requirements.

Lime dosing savings of £21k per stream.

Maintenance free – Reducing downtime otherwise spent servicing parts.

RESULT

The 12-month trial has demonstrated that they are saving 0.5 tons of lime per day per stream. At the current market price, the site is making a saving of approximately £21000 per annum, per stream.

Therefore, return on investment for the LAS 5000XD is just over one year.