Waste-to-energy (WtE) plants are traditionally designed for clean and economical disposal of waste. Design for output on the other hand was the guideline when projecting the HRC (HoogRendement Centrale) block of Afval Energie Bedrijf Amsterdam. Since commissioning of the plant in 2007, operation has continuously improved. In December 2010, the block's running average subsidy efficiency for one year exceeded 30% for the first time. The plant can increase its efficiency even further by raising the steam temperature to 480°C. In addition, the plant throughput can be increased by 10% to reduce the total cost of ownership. In order to take these steps, good preparation is required in areas such as change in heat transfer in the boiler and the resulting higher temperature upstream of the super heaters. A solution was found in the form of combining measured data with a computational fluid dynamics (CFD) model. Suction and acoustic pyrometers are used to obtain a clear picture of the temperature distribution in the first boiler pass. With the help of the CFD model, the change in heat transfer and vertical temperature distribution was predicted. For the increased load, the temperature is increased by 100°C; this implies a higher heat transfer in the first and second boiler passes. Even though the new block was designed beyond state-of-the art in waste-to-energy technology, margins remain for pushing energy efficiency and economy even further.

The formation of the nitrogen species HCN, NH 3 (N-intermediates), and NO out of fuel-bound nitrogen has a major influence on NO chemistry. Experiments have been carried out on an entrained flow reactor with pulverized wood as fuel. Staged combustion establishes a fuel-rich primary zone, where both N-intermediates and NO exist. The introduction of NRP as the ratio of the N-intermediates to NO offers a parameter that describes the nitrogen distribution in the primary zone, whereas TFN describes the overall amount of nitrogen. Air staging is an effective method for NO x reduction; the main controlling parameter is the primary air ratio, which defines both NRP and TFN. In fuel-rich conditions, NRP exceeds 1; with increased oxygen availability and temperature, the N-intermediates are depleted and NO is formed (NRP < 1). Thus, the NRP can be increased by adding NH 3 . Conventional SNCR is strongly temperature-dependent; hence, with increased temperatures, the best operation point shifts to lower air ratios. A combination of air staging and ammonia injection directly in the primary zone furthers NO x reduction, as long as it is realized in almost stoichiometric conditions. Since the reduction efficiency increases at high temperatures, the technology is called selective high temperature reduction.

Abstract:Corrosion of functional parts within waste-to-energy (WTE) plants significantly reduces their efficiency with respect to maintenance costs. Currently, nickel-based alloy claddings, several millimeters thick, are the state of the art as anti-corrosion coating. Another approach is to utilize thermally sprayed multilayer coatings with a zirconia top-coat. Lab-scale experiments under simulated WTE plant conditions and in situ tests within a WTE plant revealed a partially reduced porosity of the zirconia top-coat after the experiments, enabling the coating to act as a barrier against aggressive gases. In a lab-scale experiment sample the pores are filled up with zirconia, while the pores of the in situ samples are filled up with newly formed metal (Cr, Ni, Fe) oxides.

NO x emissions and their intermediate species NO, HCN, and NH3 have been investigated in an industrial waste-to-energy plant for the first time. Therefore, an innovative gas probe was designed accordingly to meet the challenging requirements of HCN and NH3 measurement. The N intermediates were measured in three different sample positions close to the grate. The highest concentrations were detected on the front side of the grate where the lowest local excess air ratio occurs. The NO x reduction potential, which is defined as the ratio of HCN and NH3 to NO, was above 1 during most of the relevant position sampling; hence, the selective high-temperature reduction does not seem to be a suitable technology for a further reduction of NO x emissions. The operating points investigated were conventional operation, flue gas recirculation (VLN-GM), air staging, and air staging with improved mixing. Conventional operation leads to emissions of about 450 mg/m3, which could be reduced to 200 mg/m3 by VLN-GM. Since the emissions are strongly dependent on the primary air ratio λ1, they show an almost linear correlation. The pretreatment of waste by shredding stabilizes the combustion and simplifies NO x control. The lowest emissions (around 100 mg/m3) were achieved during air-staged operation with additional air injection, due to improved mixing and the additional staging.

Plant balancing of waste-to-energy plants is a key issue in determining plant performance and operating efficiency. Traditionally, plant efficiency is determined only during the acceptance test by the means of an ex-post energy balance. For continuous operation, energy efficiency is estimated on a monthly or yearly basis using the waste throughput and average lower heating value. At Afval Energie Bedrijf in Amsterdam efficiency has to be reported on a monthly basis. Measured data from 83 positions is required to obtain the efficiency of the Hoog Rendement Central block with an ex-post energy balance on a continuous basis. This study investigated the importance of the different sensors. Efficiency calculations were performed after discarding the less important measuring positions. The measured data was replaced by the design value in the calculation. The total average margin of error per year for the efficiency value was found to be only 0.1% when the 23 most significant (instead of 83) measuring points were used, whereas individual values may differ by less than 0.5%. Operators of plants with fewer sensors can monitor their efficiency continuously if they know the most important positions.