Hanne Philbert Nielsen

The implications of chlorine-associated corrosion on the operation of biomass-fired boilers

Abstract The design of new biomass-fired power plants with increased steam temperature raises concerns of high-temperature corrosion. The high potassium and chlorine contents in many biomasses are potentially harmful elements with regard to corrosion. This paper condenses the current knowledge of chlorine-induced, high-temperature corrosion and describes the potential corrosion problems associated with burning biomass fuels either alone or in blends with coal, for electricity production. Chlorine may cause accelerated corrosion resulting in increased oxidation, metal wastage, internal attack, void formations, and loose non-adherent scales. The partial pressure of HCl in a biomass-derived flue gas, is not high enough to cause severe gas-phase corrosion attacks, but may provide scale failure and increased sulfidation of water walls in areas where locally reducing conditions occur due to poor combustion and flame impingement. The most severe corrosion problems in biomass-fired systems are expected to occur due to Cl-rich deposits formed on superheater tubes. The presence of alkali chloride salts in deposits may cause accelerated corrosion well below the melting point of the salt. The corrosion can be severe in air but may be further enhanced by SO 2 which may cause intra-deposit sulfation of the alkali chlorides liberating HCl or Cl 2 gas close to the metal surface. In case the metal surface temperature becomes high enough for molten phases to form in the deposit, the corrosion may be even further enhanced.

Influence of deposit formation on corrosion at a straw-fired boiler

Straw-fired boilers generally experience severe problems with deposit formation and are expected to suffer from severe superheater corrosion at high steam temperatures due to the large alkali and chlorine content in straw. In this study, deposits collected (1) on air-cooled probes and (2) directly at the existing heat transfer surfaces of a straw-fired boiler have been examined. Deposits collected on air-cooled probes were found to consist of an inner layer of KCl and an outer layer of sintered fly ash. Ash deposits formed on the heat transfer surfaces all had a characteristic layered structure, with a dense layer of K2SO4 present adjacent to the metal surface. It is argued that the K2SO4 layer present adjacent to the metal surface may lead to reduced corrosion rates at this boiler. A discussion of the deposit structure, the K2SO4 layer formation mechanism, and the influence of the inner layer composition on the corrosion of the superheaters is provided.

Full-scale co-firing of straw and coal

Abstract Co-firing of biofuels and coal in power plants is considered by the Danish utilities as a potential tool in reducing CO 2 emissions. To test this, full-scale measurements were carried out for 1 week on a 250 MW e pulverized coal fired unit using 10–20% straw (thermal basis). With an increased fraction of straw in the fuel, a net decrease in NO x and SO 2 emissions was measured. The SO 2 emission decreased partly due to the lower sulfur content of the fuel per MJ, but also due to higher sulfur retention in the ash. The NO emission decreased solely due to lower conversion of fuel-N. An increased fraction of straw in the fuel blend resulted in a higher potassium content, but no significant increase in slagging or fouling was observed. Only small amounts of deposit at the lower part of the radiant superheater and little slagging at the furnace walls were observed as a result of co-firing straw and coal. No significant effects on the performance of the desulfurization plant were detected, which may be due to the short test period, probably not allowing the desulfurization process to reach steady-state operation.

Tuning quadratic nonlinear photonic crystal fibers for zero group-velocity mismatch

A nonlinear index guiding silica PCF is optimized for efficient second harmonic generation through dispersion calculations zero group velocity mismatch is possible for any pump wavelength above 80 nm. Very high conversion efficiencies and bandwidths are found.

Deposition and Corrosion in Straw- and Coal-Straw Co-Fired Utility Boilers

Department of Chemical Engineering, Technical University of Denmark Building 229, DK-2800 Lyngby, Denmark Phone: +45 45 25 28 83, Fax: +45 45 88 22 58, E-mail: ff/hpn/paj/lah/hl/kdj@kt.dtu.dk Midtkraft I/S Power Company, Studstrup Power Station, DK-8541 Skodstrup, Denmark. Phone: +45 86 99 17 00, Fax: +45 86 99 37 20 E-mail: pbh@midtkraft.dk,kha@kt.dtu.dk (1) Currently with Rockwool International A/S, DK-2640 Hedehusene, Denmark. (2) Currently with SunChemical A/S, DK-4600 Koge, Denmark. Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen NV, Denmark. Phone: +45 38 14 20 00, Fax: +45 33 63 39 89 E-mail: hss@geus.dk Currently with Danfoss A/S, DK-6430 Nordborg, Denmark. Faelleskemikerne, I/S Fynsvaesrket, Havnegade 120, DK-5000 Odense C, Denmark. Phone: +45 65 90 44 44, Fax: +45 65 90 38 12 Faelleskemikerne, ElsamProjekt A/S, Kraftvaerksvej 53, DK-7000 Fredericia, Denmark Phone: +45 79 23 33 33, Fax: +45 75 56 44 77 E-mail: bos/nh@elsamprojekt.dk Elkraft A.m.b.a., Lautruphoj 5–7, DK-2750 Ballerup, Denmark Phone: +45 44 66 00 22, Fax: +45 44 65 61 04

Measurement Properties of the SEAM Questionnaire Using Rasch Analysis on Data From a Representative Danish Sample of 0- to 6-Year-Olds:

In the current study, the strength-based questionnaire Social-Emotional Assessment/Evaluation Measure (SEAM)–Research Edition was for the first time applied in a nationally representative sample of 0- to 6-year-old children. The focus of this study was the measurement properties of a Danish adaptation of SEAM. Rasch analysis was used to examine the criterion-related construct validity as well as accuracy and reliability of the measurement. The primary goal was to determine whether the 10 SEAM benchmarks could be combined into one total score or into a limited number of subscores. Data were collected by child-care providers in nonparental child-care facilities, and the response rate was high (95%; N = 9,827). The 10 benchmarks were successfully combined into two overall indexes: Empathy and Self-regulation & Cooperation. The reliability coefficients ranged from adequate (0.79) to excellent (0.94). However, standard errors of measurements were relatively large for the two indexes.

Simultaneous phase- and group-velocity matching in photonic crystal fibres

We investigate the possibility of designing a triangular index-guiding photonic crystal fiber having simultaneous phase- and group-velocity matching for second-harmonic generation. A lower limit on the phase-velocity mismatch for perfect group-velocity matching is estimated.