Influence of air-staging on the concentration profiles of NH3 and HCN in the combustion chamber of a CFB boiler burning coal

The characterisation of the concentration profiles of NH3 and HCN are of great importance for increasing the knowledge of the formation and destruction pathways of NO and N2O in a fluidized bed boiler. Further improvements of the sampling methods for the determination of both NH3 and HCN in the combustion chamber in full-scale CFB boilers are also needed. A gas-sampling probe connected to a Fourier Transform Infra Red (FTIR) instrument and a gas-quenching (GQ) probe in which the sample is quenched directly in the probe tip by a circulating trapper solution were used. The FTIR technique is based on analysis of hot combustion gases, whereas the trapper solutions from the GQ probe were analysed by means of wet chemistry. The tests were performed during coal combustion in a 12 MW CFB boiler, which was operated at three air-staging cases with the addition of limestone for sulphur capture. The concentration profiles of NH3 and HCN in the combustion chamber showed a different pattern concerning the influence of air-staging. The highest levels of NH3 were observed during reducing conditions (severe air-staging), and the lowest were found under oxidising conditions (no air-staging). The levels of HCN were much lower than those measured for NH3. The highest levels of HCN were observed for reversed air-staging and severe air-staging showed almost no HCN. The potential reactions involving NH3 and HCN in the combustion chamber as well as the potential measurement errors in each sampling technique are discussed for the three air-staging cases

Toxic effects of phenothiazines on the eye

Publications about the retinotoxic action of phenothiazine derivatives led the author to undertake an ophthalmological investigation in two psychiatric hospitals in The Netherlands. The pharmacological actions of phenothiazine preparations are listed and a survey of the phenothiazine derivatives which are at present in use is given. Some retinotoxic substances are discussed and a survey is given of the literature on the ocular complications of phenothiazine therapy. The eyes of 561 patients were examined. of whom 541 are included in this study. 343 of these patients(63.4 %) were found to have retinopathy. The correlation between the retinopathy and the total dose of phenothiazine preparations taken. and between the retinopathy and the duration of treatment. was highly significant. The correlation between the retinopathy and the average daily dose taken was significant. The retinopathy was associated with a reduced standing potential of the eye. as determined by electro-oculography. It was possibly responsible for diminished visual acuity in some cases, and for an abnormally large proportion of protans in the group of patients with colour defects. It was not possible to ascribe a more severe retinotoxic action to one or more specific phenothiazine derivatives than to others. In the author's opinion regular examination of the eyes of patients who are being treated with phenothiazine preparations in high dosage and for for a long period of time is indicated

Strategies to reduce gaseous KCl and chlorine in deposits during combustion of biomass in fluidised bed boilers

Combustion of a biomass with an enhanced content of alkali and chlorine (Cl) can result in operational problems including deposit formation and superheater corrosion. The strategies applied to reduce such problems include co-combustion and the use of additives. In this work, measures were investigated in order to decrease the risk of superheater corrosion by reducing gaseous KCl and the content of chlorine in deposits. The strategies applied were sulphation of KCl by sulphur/sulphate containing additives (i.e. elemental sulphur (S) and ammonium sulphate (AS)) and co-combustion with peat. Both sulphation of KCl and capture of potassium (K) in ash components can be of importance when peat is used. The experiments were mainly performed in a 12 MW circulation fluidised bed (CFB) boiler equipped for research purposes but also in a full-scale CFB boiler. The results were evaluated by means of IACM (on-line measurements of gaseous KCl), conventional gas analysis, deposit and corrosion probe measurements and ash analysis.Ammonium sulphate performed significantly better than elemental sulphur. Thus the presence of SO3 (i.e. AS) is of greater importance than that of SO2 (i.e. S) for sulphation of gaseous KCl and reduction of chlorine in deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion with peat although chlorine in the deposits was greatly reduced. This reduction was supposedly due to capture of K by reactive components from the peat ash in parallel to sulphation of KCl. These compounds remained unidentified. The effect of volatile combustibles on the sulphation of gaseous KCl was investigated. The poorest sulphation was attained during injection of ammonium sulphate in the upper part of the combustion chamber during the lowest air excess ratio. The explanation for this is that SO3 was partly consumed by side reactions due to the presence of combustibles. These experimental results were supported by modelling, although the sulphation of KCl in the presence of combustibles were somewhat overestimated in the chemical kinetic model. Oxygen also had an effect on the sulphation when injecting AS in the cyclone. Less gaseous KCl was reduced during air excess ratio λ = 1.1 compared to the higher air excess ratios. A correlation was also observed between the sulphation of gaseous KCl and reduced chlorine content in the deposits

Strategies to reduce gaseous KCl and chlorine in deposits during combustion of biomass in fluidised bed boilers

Combustion of a biomass with an enhanced content of alkali and chlorine (Cl) can result in operational problems including deposit formation and superheater corrosion. The strategies applied to reduce such problems include co-combustion and the use of additives. In this work, measures were investigated in order to decrease the risk of superheater corrosion by reducing gaseous KCl and the content of chlorine in deposits. The strategies applied were sulphation of KCl by sulphur/sulphate containing additives (i.e. elemental sulphur (S) and ammonium sulphate (AS)) and co-combustion with peat. Both sulphation of KCl and capture of potassium (K) in ash components can be of importance when peat is used. The experiments were mainly performed in a 12 MW circulation fluidised bed (CFB) boiler equipped for research purposes but also in a full-scale CFB boiler. The results were evaluated by means of IACM (on-line measurements of gaseous KCl), conventional gas analysis, deposit and corrosion probe measurements and ash analysis.Ammonium sulphate performed significantly better than elemental sulphur. Thus the presence of SO3 (i.e. AS) is of greater importance than that of SO2 (i.e. S) for sulphation of gaseous KCl and reduction of chlorine in deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion with peat although chlorine in the deposits was greatly reduced. This reduction was supposedly due to capture of K by reactive components from the peat ash in parallel to sulphation of KCl. These compounds remained unidentified. The effect of volatile combustibles on the sulphation of gaseous KCl was investigated. The poorest sulphation was attained during injection of ammonium sulphate in the upper part of the combustion chamber during the lowest air excess ratio. The explanation for this is that SO3 was partly consumed by side reactions due to the presence of combustibles. These experimental results were supported by modelling, although the sulphation of KCl in the presence of combustibles were somewhat overestimated in the chemical kinetic model. Oxygen also had an effect on the sulphation when injecting AS in the cyclone. Less gaseous KCl was reduced during air excess ratio λ = 1.1 compared to the higher air excess ratios. A correlation was also observed between the sulphation of gaseous KCl and reduced chlorine content in the deposits

Nitrogen containing additives for simultaneous reduction of KCl and NOx during biomass combustion

Abstract -High levels of alkali chlorides in the flue gas can cause enhanced deposit formation and superheater corrosion during combustion of biofuels. These alkali chlorides mainly originate from potassium chloride (KCl). A challenge during combustion of biofuels is to simultaneously reduce NOx and KCl. The ChlorOut concept has been developed by Vattenfall to minimise deposit formation and corrosion. It consists of IACM, an instrument for on-line measurements of gaseous alkali chlorides, and a sulphate-containing additive that converts alkali chlorides to less corrosive alkali sulphates. The sulphate-containing additive is often ammonium sulphate, (NH 4 ) 2 SO 4 , and, therefore, a significant NOx reduction is also achieved. This paper presents the results from a comparison of the conventional SNCR additives (ammonia or urea) and (NH 4 ) 2 SO 4 for reduction of NOx and/or KCl during combustion in a CFB boiler. The fuel consisted of either a mixture of wood chips and wood pellets with added PVC or with straw pellets. Of special interest was the influence of sulphation of KCl in parallel to the reduction of NO and if these processes interact. The results show that there are rather small differences in performance concerning NOx reduction between the additives

Simultaneous reduction of NO and KCl during injection of ammonium sulphate in a biomass fired BFB boiler

Sulphate containing additives, such as ammonium sulphate (AS), are used for sulphation of KCl during biomass combustion. Another aspect with injection of AS is that a significant NOx reduction is achieved but it may also have an impact on other flue gas components. Operating parameters such as the air excess ratio and the presence of combustibles could also have an effect on the flue gas chemistry involving NO and KCl. This paper is based on results obtained from a measurement campaign during combustion of demolition wood in a 63 MWth Bubbling Fluidised Bed (BFB) boiler. Ammonium sulphate was injected for simultaneous reduction of NO and KCl at two positions in the boiler i.e. in the upper part of the combustion chamber and in the empty pass. The impact of AS on the flue gas chemistry was investigated at different operating conditions. Several measurement tools including, IACM (online measurements of gaseous alkali chlorides) and gas analysis were applied. The position for injection of AS as well as the operating parameters had an impact on the flue gas chemistry for reduction of both NO and KCl

Aspects on the Flue Gas Chemistry of KCl, NO and CO During Injection of Ammonium Sulphate - An Experimental Approach

Sulphate containing additives, such as ammonium sulphate (AS, (NH4)2SO4), are used for sulphation of KCl during biomass combustion. Another aspect with injection of AS is that a significant NOx reduction is achieved but it may also have an impact on other flue gas components such as CO. The concentration of oxygen and the presence volatile combustibles could also have an effect on the flue gas chemistry involving KCl, NO and CO. This paper is based on results obtained from two measurement campaigns during co-combustion of wood chips and straw pellets in a 12 MW circulating fluidised bed (CFB) boiler. In the first campaign, the NO reduction performance of AS, ammonia and urea was compared. In the second one, AS was injected at three positions in the boiler i.e. in the upper part of the combustion chamber, in the cyclone inlet, and in the cyclone. The impact of AS on the flue gas chemistry was investigated at three air excess ratios (λ= 1.1, 1.2 and 1.4). Several measurement tools including, IACM (on-line measurements of gaseous alkali chlorides) and gas analysis were applied. The position for injection of AS as well as the different air excess ratios had a great impact on the flue gas chemistry for especially KCl and NO