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Gas cleaning at high temperatures
TECHNOLOGY ELSEVIER
Powder Technology
80 (1994) 275-276
Book Review
Gas Cleaning at High Temperatures Edlted by R Chft and J.P K Sevdle, published by Blackle Academx and ProfessIonal, Glasgow, 1993, 696 pp , f99.00, ISBN 0-71540178.
This excellent book comprises the papers presented at the Second International Symposium on Gas Cleaning at High Temperatures held at the University of Surrey on 27-29 September 1993. The book is substantial: in 686 pages 42 papers are presented, divided into three groups: 6 in Section 1 on Inertial Separators and Electrostatic Precipitators; 21 m Section 2 on Filters; and 15 in Section 3 on Chemical Separations. The first Symposium, also at the University of Surrey, was held in 1986, and it is interesting to compare the changes in the intervening seven years. The drivers have changed, of course: the environmental requirements continue to tightened up, although they still differ significantly from country to country. The contaminants of most concern have also changed: in 1986, the oxides of sulfur were of most concern, and particulate emissions were of concern primarily in relation to opacity and respiratory health. Today, the chemical component of combustion that is of predominant concern is the oxides of nitrogen; global warming is an issue; and in the future CO, emissions may become important. As a result, the contrast between the two meetings is considerable. In the earlier meeting, the first six of 31 papers were concerned with inertial separators (a later paper should also have been included in this classification); five were concerned with measuring techniques; six with ceramic filters, the major interest being directed towards fabric filter media; five papers relating to electrostatic effects; three relating to granular beds; and the remainder concerned with comparisons of different techniques. Only particle separation techniques were discussed m any detail; with the exception of two papers relating to alkali removal, there was no discussion of any chemical cleaning. In the Proceedings of the 1993 meeting; there are four papers on inertial separators and only one on electrostatic separation: it appears that at the moment the earlier disappomtements have discouraged attempts to develop high-temperature electrostatic precipitators, or to look at electrostatic enhancement of other techniques. The major particle separation technology
003%5910/94/$07 00 0 1994 Elsevler SSDI 0379-6779(94)0285B-N
Science
SA
All rights reserved
that is discussed here related to the use of rigid ceramic filters - ‘candles’ and cross-flow filter elements - in both pressurized fluidized bed combustors (PFBC) and coal gasification applications. Only three papers expressely discuss PFBC applications, although there are currently at least six relatively large-scale demonstration-sized tests underway: the only one of these that is discussed here is the Grimethorpe rig, which has now closed down It is a pity that the operators of the other large-scale PFBC demonstrations did not share their recent experience at the meeting. There are three papers related to the removal of particulate from the product-gas of coal gaslfiers. As has been pointed out, the gas temperature is typically significantly lower than for PFBC apphcattons. This may be an advantage in terms of candle durability, but the metalhc parts of the support structure and the blow-back system may present problems. a paper by Zievers et al. dtscusses the possibility of using ceramic structural components. There have been problems with ash build-up in a number of the larger systems, certainly those associated with PFBCs. This issue is mentioned a few times in these Proceedings, and tt is noted that different feedstocks may behave in different ways, but there is limited discussion of the whole issue of solids handling. Filter experience m the off-gas from incinerators, boilers and catalytic regenerators is described There are also some papers describing laboratory results, all with oxtdlzing carrier gases. Of the possible filter media, twelve papers in these Proceedings are concerned principally with candle-type filters, which appears currently to be the configuration of choice for most of the applications Only one paper discusses the NextelTM ceramic fiber filter bags, which is a little surprising in view of the fairly considerable amount of satisfactory service history that is now available. There are two papers on cross-flow filters, but as yet there 1s little long-term operational history: the issues of durability and cleanability are only currently being addressed. There is also a single paper concerned with porous metal filters, and another reporting experience with metal-fiber bags. Finally, there are three papers discussing experience with granular bed filters (GBF). In view of the earlier problems with
276
Book Review I Powder Technology 80 (1994) 275-276
moving-bed GBF operated under PFBC conditions, this paper (by Zevenhoven et al.) is particularly interesting; but their conclustons are again largely negative. The most important difference between this Conference and the 1986 one 1s the attention given here to the chemical aspects of hot gas cleaning. Sixteen papers address this aspect, of which nine are mainly concerned with sulfur removal. Six papers are prmcipally concerned with the removal of contaminants from gasifier off-gas, the remainder principally with combustion gases of various sorts. Several papers concerned with the conversion of combustion of coal mention the effects of chlorides in the coal on the chemistry, and this is an important factor on which there has previously been relatively little informatron. There are two papers on the use of membranes for separation, and this is an interesting development. It seems likely that the declassification of the extensive research on membranes for gaseous separations connected with nuclear weapon development may lead to a considerable expansion of interest in this technology over the next few years. All in all, this is a large collection of generally highquality papers, and, hke its predecessor, these Proceedmgs will be an important archive for those
concerned with thus field for several years. I am a little disappointed at the lack of papers concerned with the engineering of large filter systems, since, as recent experience with PFBC filters has shown, this aspect is frequently at least as important as the behavior of the filter medium itself. The expansion in the section concerned with chemical cleaning 1s valuable, although this would probably have been helped by a review paper to descrrbe the current state of knowledge, particularly m areas involving technologies other than those of interest to the community to which this volume is addressed. The book itself 1s handsome and well-produced. However, as a general comment, I feel that these Proceedings which are intended to have a significant archival life, would have benefitted very greatly from name and subject indices. Finally, in the Preface, the Editors report that there was on opening address from Professor Dr Ing Friedrrch Liiffler. I am sure that those of us who were unable to attend the meeting Itself would have liked that address to be included in the Proceedings. John
Strmger EPRI Palo Alto, CA, USA
Powder Technology
80 (1994) 275-276
Book Review
Gas Cleaning at High Temperatures Edlted by R Chft and J.P K Sevdle, published by Blackle Academx and ProfessIonal, Glasgow, 1993, 696 pp , f99.00, ISBN 0-71540178.
This excellent book comprises the papers presented at the Second International Symposium on Gas Cleaning at High Temperatures held at the University of Surrey on 27-29 September 1993. The book is substantial: in 686 pages 42 papers are presented, divided into three groups: 6 in Section 1 on Inertial Separators and Electrostatic Precipitators; 21 m Section 2 on Filters; and 15 in Section 3 on Chemical Separations. The first Symposium, also at the University of Surrey, was held in 1986, and it is interesting to compare the changes in the intervening seven years. The drivers have changed, of course: the environmental requirements continue to tightened up, although they still differ significantly from country to country. The contaminants of most concern have also changed: in 1986, the oxides of sulfur were of most concern, and particulate emissions were of concern primarily in relation to opacity and respiratory health. Today, the chemical component of combustion that is of predominant concern is the oxides of nitrogen; global warming is an issue; and in the future CO, emissions may become important. As a result, the contrast between the two meetings is considerable. In the earlier meeting, the first six of 31 papers were concerned with inertial separators (a later paper should also have been included in this classification); five were concerned with measuring techniques; six with ceramic filters, the major interest being directed towards fabric filter media; five papers relating to electrostatic effects; three relating to granular beds; and the remainder concerned with comparisons of different techniques. Only particle separation techniques were discussed m any detail; with the exception of two papers relating to alkali removal, there was no discussion of any chemical cleaning. In the Proceedings of the 1993 meeting; there are four papers on inertial separators and only one on electrostatic separation: it appears that at the moment the earlier disappomtements have discouraged attempts to develop high-temperature electrostatic precipitators, or to look at electrostatic enhancement of other techniques. The major particle separation technology
003%5910/94/$07 00 0 1994 Elsevler SSDI 0379-6779(94)0285B-N
Science
SA
All rights reserved
that is discussed here related to the use of rigid ceramic filters - ‘candles’ and cross-flow filter elements - in both pressurized fluidized bed combustors (PFBC) and coal gasification applications. Only three papers expressely discuss PFBC applications, although there are currently at least six relatively large-scale demonstration-sized tests underway: the only one of these that is discussed here is the Grimethorpe rig, which has now closed down It is a pity that the operators of the other large-scale PFBC demonstrations did not share their recent experience at the meeting. There are three papers related to the removal of particulate from the product-gas of coal gaslfiers. As has been pointed out, the gas temperature is typically significantly lower than for PFBC apphcattons. This may be an advantage in terms of candle durability, but the metalhc parts of the support structure and the blow-back system may present problems. a paper by Zievers et al. dtscusses the possibility of using ceramic structural components. There have been problems with ash build-up in a number of the larger systems, certainly those associated with PFBCs. This issue is mentioned a few times in these Proceedings, and tt is noted that different feedstocks may behave in different ways, but there is limited discussion of the whole issue of solids handling. Filter experience m the off-gas from incinerators, boilers and catalytic regenerators is described There are also some papers describing laboratory results, all with oxtdlzing carrier gases. Of the possible filter media, twelve papers in these Proceedings are concerned principally with candle-type filters, which appears currently to be the configuration of choice for most of the applications Only one paper discusses the NextelTM ceramic fiber filter bags, which is a little surprising in view of the fairly considerable amount of satisfactory service history that is now available. There are two papers on cross-flow filters, but as yet there 1s little long-term operational history: the issues of durability and cleanability are only currently being addressed. There is also a single paper concerned with porous metal filters, and another reporting experience with metal-fiber bags. Finally, there are three papers discussing experience with granular bed filters (GBF). In view of the earlier problems with
276
Book Review I Powder Technology 80 (1994) 275-276
moving-bed GBF operated under PFBC conditions, this paper (by Zevenhoven et al.) is particularly interesting; but their conclustons are again largely negative. The most important difference between this Conference and the 1986 one 1s the attention given here to the chemical aspects of hot gas cleaning. Sixteen papers address this aspect, of which nine are mainly concerned with sulfur removal. Six papers are prmcipally concerned with the removal of contaminants from gasifier off-gas, the remainder principally with combustion gases of various sorts. Several papers concerned with the conversion of combustion of coal mention the effects of chlorides in the coal on the chemistry, and this is an important factor on which there has previously been relatively little informatron. There are two papers on the use of membranes for separation, and this is an interesting development. It seems likely that the declassification of the extensive research on membranes for gaseous separations connected with nuclear weapon development may lead to a considerable expansion of interest in this technology over the next few years. All in all, this is a large collection of generally highquality papers, and, hke its predecessor, these Proceedmgs will be an important archive for those
concerned with thus field for several years. I am a little disappointed at the lack of papers concerned with the engineering of large filter systems, since, as recent experience with PFBC filters has shown, this aspect is frequently at least as important as the behavior of the filter medium itself. The expansion in the section concerned with chemical cleaning 1s valuable, although this would probably have been helped by a review paper to descrrbe the current state of knowledge, particularly m areas involving technologies other than those of interest to the community to which this volume is addressed. The book itself 1s handsome and well-produced. However, as a general comment, I feel that these Proceedings which are intended to have a significant archival life, would have benefitted very greatly from name and subject indices. Finally, in the Preface, the Editors report that there was on opening address from Professor Dr Ing Friedrrch Liiffler. I am sure that those of us who were unable to attend the meeting Itself would have liked that address to be included in the Proceedings. John
Strmger EPRI Palo Alto, CA, USA