Select Committee on European Communities Eleventh Report


49. Evidence from the waste management industry, the EWA, the cement industry and the power industry painted a generally consistent picture of the main technical implications of the draft Directive. These would require:

  • Upgrading of gas cleaning equipment to reduce NOx;
  • Operation to ensure that total organic carbon (TOC) of the slag and bottom ashes is less than 3 per cent of the material's dry weight;
  • Upgrading or installation of aqueous treatment facilities; and
  • Investment in technologies for non-dedicated waste incineration plant (i.e. co-incineration plant) to reduce resulting emissions.

50. Of these the main technical issue considered by the enquiry was the proposed NOx limits and the technologies for meeting them, with particular reference to the cement industry (see box). The UK cement industry is particularly affected by the proposals because of the large number of manufacturing plants which use the wet process[15] (of 33 kilns currently operated by BCA members, 18 use wet or semi-wet processes). The BCA claimed that no technology currently existed for wet process kilns which could guarantee NOx reduction below 800mg/m3 as a daily average: "new technologies have driven emissions lower but at a cost of economic and environmental burdens, from the technique itself, that give benefits that are imperceptible in contributing to the national air quality strategy" (p 51). Rugby Cement gave a detailed explanation of the difficulty of reaching the proposed NOx limit (pp 178-9).


Due to the very high temperatures in the main flame of the rotary kiln, nitrogen oxides are formed by oxidation of molecular nitrogen in the combustion air ("thermal NOx"). Thermal NOx formation is strongly dependent on the combustion temperature, with a marked increase above 1400oC. "Hard" burning required by certain raw mixes—i.e. at a higher temperature profile—increases NOx formation.

While thermal NOx is the dominant contribution to total NOx generation, a smaller part may also result from nitrogen compounds contained in the fuels which are oxidised in the flame ("fuel NOx"). In the main burner flame, the contribution of fuel NOx is much lower than the thermal NOx.

In the secondary firing of a preheater/precalciner kiln with a flame temperature of not more than 1200oC, the formation of thermal NOx is much lower compared to the main burner flame. Therefore, in precalciner kilns, where up to 60% of the total fuel can be burnt in the calciner flame, fuel NOx may contribute significantly to the total NOx emissions.

Natural raw materials, such as clays or shales, may also contain nitrogen compounds. Part of these compounds may be released and oxidised upon heating in the kiln system and may thus in certain cases contribute significantly to the total NOx emissions ("raw materials NOx").

NOx formation is reduced if fuel is burnt in a more "reducing" atmosphere with low oygen content. Operation under reducing conditions is limited due to process requirements to maintain good clinker quality and undisturbed kiln operation.

NOx emissions from cement kilns (expressed as NO2) typically vary between 500 and 2000 mg/Nm3.

Source: European Cement Association (Cembureau) (see p 70)

51. A relatively straightforward and inexpensive method of reducing NOx is the use of ammonia or urea in the so-called Selective Non-Catalytic Reduction (SNCR) process (see box). The process is used by a number of cement firms in the UK (p 69), and is suitable for other combustion plants, although in the case of the waste incineration industry only one example of its current use was identified to us—the SELCHP plant in South East London. Concern was, however, expressed by, among others, the ESA and the NSCA at the health and safety implications of SNCR. Storage of ammonia had the potential for bringing a site within the "major hazard" definition and its use in the SNCR process risked causing harmful emissions, or "ammonia slip" (QQ 78, 273). We understand that a large municipal waste incineration plant would need to use about 10 tonnes of ammonia per week.


SNCR is a technique that involves the injection of ammonia or urea into the combustion process at an appropriate point. The hydrogen in the ammonia combines with the oxygen in the NOx to form water vapour, leaving the nitrogen atoms from the ammonia and NOx to from N2.

The temperature range within which the reactions will take place is very limited—around 800 to 900oC. The exact point of ammonia injection is critical. If the ammonia is injected at too high a temperature it is burnt by excess air and does not achieve a reduction in NOx. If it is injected at too low a temperature then little ammonia reacts, and the unreacted gas is discharged to atmosphere—highly undesirable from the environmental point of view.

Source: evidence from Rugby Cement (p 179); see also evidence from SELCHP (p 184).

52. It became apparent during the enquiry that there was a lack of scientific evidence on the costs and benefits of ammonia injection; and that full life-cycle assessment (LCA) of ammonia production and use was not being carried out. The DETR, in a supplementary note (based on calculations by the Environment Agency) informed us that between 175 and 320 grammes of NOx were emitted from the manufacture of 1 tonne of ammonia—the amount of ammonia required to abate 2 tonnes of NOx from incinerator emissions (p 118). Mr Michael Theben, DG XI, commented that it was very difficult to find a LCA which covered everything: the basic approach of the proposal was not to provide for specific techniques, merely to set ELVs and to leave it to the operator whether to use SNCR or alternative NOx reduction methods (Q 516).

53. The IChemE questioned the practice of injecting ammonia and urea: "These chemicals can have their own impact on the environment, so their introduction where they did not exist before is another questionable environmental step." (p 170) Professor Porteous criticised an "overzealous" approach to NOx control, given the small contribution of incineration to total NOx burdens (p 176). Mr Bill Prescott, of the Onyx Group (which operates SELCHP) and representing the ESA, drew attention to the high cost of retrofitting SNCR (around £2 million for SELCHP) and said the waste management industry's view was that the case for introducing a new pollutant into the flue gases was not proven: "We have consistently held that the Commission should look at a cost-benefit analysis of the introduction of ammonia to reduce the NOx to the levels that they are proposing….It seems to us that the figure of 200 (mg/Nm3) is something that has been plucked out of the air, probably to meet the technologies which are being supplied, i.e. for commercial reasons rather than for regulatory or environmental reasons." (Q 78)

54. A number of witnesses (SEPA, Scottish Power, the British Plastics Federation and the cement industry) argued that the proposed NOx limits could inhibit multi-fuel use. The BCA said that the industry might have to return to full fossil-fuel use, with consequent environmental impacts; the co­incineration of tyres (which a 1998 report by the Environment Agency recognised as BPEO) could be halted (p 52).


55. The cost-benefit analyses prepared by ENTEC for the DETR's Regulatory and Environmental Impact Assessment suggested that there would be net benefits in applying the proposed standards to most types of incinerators including co-incineration. No benefit, however, could be demonstrated for sewage sludge incineration. As we have already noted in Part 1 of this Report (paragraph 0), the analyses have considerable limitations.

56. The EWA did not believe that the cost-benefit case for changes to the current Directives had been adequately made. These would involve investment of £ 1-2 million per plant (pp 81-2). Aspinwall and Company, similarly, were not sure that the benefits of NOx limits and the required upgrading outweighed the costs(p 135). CSERGE felt that the Commission's cost-benefit analysis did not include all impacts from emissions: "In view of the scientific uncertainty a more stringent precautionary approach would seem to be appropriate." (p 139) ERM argued that cost-benefit analysis should "be used more appropriately at the outset to inform the decision process"; they suggested that to date the cost-benefit analyses applied had not examined the marginal costs and benefits and that decision-makers therefore had an incomplete picture of the likely impacts of the Directive (pp 162-3).


57. Article 4 of the draft Directive requires that the heat generated during the incineration process is recovered as far as possible. Evidence from the waste industry, in particular the EWA, revealed a sense of frustration that, despite strong efforts, it had proved difficult to introduce new combined heat and power (CHP) capacity at waste incineration plants. The main problems appeared to relate to the need to bring together a range of different parties and that many aspects were outside the control of the industry (Q 338). We note that to date no market had been found for heat from one of the largest and most modern waste incineration plants in Europe, SELCHP, which (as its full name implies[16]) was designed to provide both heat and power, and is located in an area of South East London where some potential for district heating schemes might have been expected; at present it only supplies power to the grid. Mr Meacher said it was a matter of concern that only some three per cent of existing CHP plants in the UK used waste as fuel; he found the situation of SELCHP worrying, whilst acknowledging that to insist on CHP being provided at every new incinerator (as the European Parliament was proposing) could be counter-productive (QQ 474-7).

15   The cement manufacturing process can be described as either "wet" or "dry", depending on whether the raw materials (limestone or chalk, with shale or clay) are prepared as a slurry or as a dry powder. Back

16   South East London Combined Heat and Power. Back

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