Are Incinerator Rules Suspended during Start-up and Shut-down?

Sampling requirements and gas-cleaning (anti-NOx, bag filters, activated carbon addition) are largely suspended over the many hours start-up and shut down, but these days pre-heating eg. by oil/diesel is required for cold-start, before any waste is loaded in.

Wang et al. reported measurements from a Swedish incinerator cold restart early last year:
“PCDD/F measurements of incinerators only have to be conducted once or twice annually and are usually under normal and good operational conditions. Well over a 1000-fold increase in PCDD/F concentration and a two-fold increase in annual PCDD/F emission during the start-up procedures. The days when a cold start-up occurs will thus be much more significant than on the other days of normal operations.”

The problem is still poorly understood. Part arises from dioxins and diooxin-precursors condensing on internal surfaces and emitted during the extended start-up, giving a “memory effect”. Warm restart as in daily-intermittent operation for supplying heat is likely to be far worse for dioxin totals, yet our Env Agency continues to argue for CHP regardless.

The attached Abstracts of two recent studies show the problem is being taken seriously outside the UK.

Influence of start-up on PCDD/F emission of incinerators
Lin-Chi Wang et al. Chemosphere 67 (2007) 1346–1353 Available online 8 January 2007

Abstract – This study aims to evaluate the influence of start-up on polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) concentration in the stack flue gas of incinerators and its contributing PCDD/F emission. The PCDD/F emission of the first sample among three consecutive stack flue gas samples of five intermittent incinerators, which sampled at a stable combustion condition after start-up, is 2–3 times higher than the mean of the others. For verifying the PCDD/F characteristics of incinerators during start-up, one continuous MSWI was investigated for two years. The elevated PCDD/F emissions of the MSWI during start-up could reach 96.9 ng I-TEQ N m_3 and still maintained a high PCDD/F emission (40 times higher than the Taiwan emission limit) even 18 h after the injection of activated carbon, indicating the memory effect. Taking the MSWI for example, which consists of four incinerators, the estimated annual PCDD/F emission from normal operational conditions was 0.112 g I-TEQ. However, one start-up procedure can generate _60% of the PCDD/F emissions for one whole year of normal operations. And the PCDD/F emission, which is the result of the start-ups of four incinerators, was at least two times larger than that of a whole year’s normal operations, without consideration for the PCDD/F emission contributed by the long lasting memory effect.

Characteristics of dioxin emissions at startup and shutdown of MSW incinerators
Hajime Tejima et al. Chemosphere 66 (2007) 1123–1130 Available online 24 July 2006

Abstract – Dioxin concentrations from municipal waste incinerators in Japan and elsewhere often show low concentrations that comply with legal limits (in this paper, the term ‘‘dioxin’’ designates WHO-TEQ: PCDD/Fs + dioxin-like PCB). However, such data is usually generated under normal steady state operational conditions, and there has been little investigation of releases occurring during startup and shutdown. It is important, therefore, to ascertain quantitatively emissions in an unsteady state (startup and shutdown) in order to correctly evaluate the relationship between emissions from a facility and the surrounding environment. The present study aimed to examine dioxin emissions of a continuously operated incinerator at startup and shutdown, and estimating the time period of greatest emission, and the processes causing dioxin generation. The startup process was divided into five stages and the shutdown into two; at each stage, dioxins in the flue gas were measured at the boiler outlet and the stack. From the concentration of dioxins and the flue gas volume at each stage, the amount of dioxins at startup and shutdown were calculated, and these were compared with that under steady state conditions. Dioxin concentration at the stack under steady state conditions was a very low level, while those at startup and shutdown were higher. In the case where dioxin concentration under a steady state is a low like in this study, it is indicated that the total annual dioxin emission from a facility could be attributed to the startup periods.

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