GC 10: Applied Technology
With increasing requirements to control emissions to the atmosphere and with the development of more advanced technologies, the areas of application of gas cleaning are constantly being extended into more demanding environments. This report reviews gas cleaning technology under a range of hostile and difficult conditions. First, the effects of temperature and pressure on the basic collection mechanisms are discussed. The types of process requiring gas cleaning at high temperatures and pressures are reviewed and the range of application and the limitations of cyclones, scrubbers, filters and electrostatic precipitators are reviewed. The factors affecting erosion and corrosion in the various components of gas cleaning equipment are then summarised and precautionary measures commonly adopted described. Particular attention is given to humidity and the calculation of acid dewpoints associated with combustion products. A section is then devoted to the way that the performance of gas cleaning equipment can be significantly affected by the physical nature of the bulk collected dust, both in the way that it adheres to the machinery surfaces and in its ability to form a strong compacted deposit. This is a topic which has not received much attention elsewhere in the literature.
In some gas cleaning applications the particle concentrations that are acceptable in the cleaned gas are very low. This may be because the contaminant is extremely toxic either to personnel or to biochemical processes, or because the presence of particles in mechanical components of delicate instruments is deleterious. Such high levels of gas cleanliness are achieved, almost exclusively, by using fibrous filters although the present report does consider the limitations of other devices. The levels of contamination, the required cleaning efficiencies and the general management of air flows is considered for a number of applications. These include: toxic dusts, radioactive particulates, air sterilisation (for biochemical processes), ventilation, air conditioning and clean rooms. Cyclones, scrubbers, bag filters and electrostatic precipitators are all considered but the major interest is in fibrous filters. These are considered in two classes. The first class is used for ventilation and air conditioning applications and the various designs, performance characteristics and methods of operation are described. The second class or HEPA (High Efficiency Particulate Air) filters can achieve collection efficiencies in excess of 99.99% for all particles. Their construction, installation, operation, performance and disposal are discussed in detail. Both classes of fibrous filter are required to conform to strict requirements which necessitates rigorous testing. A number of test procedures have been developed using different test rigs, different aerosols and different methods of measuring penetration. The various test procedures are examined in some detail and their relative merits discussed.
Since the mid 1970ís a great deal of research has been conducted with a view to solving the problems associated with cleaning the combustion gases produced by advanced designs of coal fired power plants. Such gases, derived from fluidised bed combustors for example, may be at temperatures up to 1300 K and pressures up to 15 bar. Extra efficiency of coal to electricity conversion may be obtained by expanding these gases directly through a turbine. The economic success of such advanced power generation projects depends crucially on the degree to which the gases can be cleaned hot. A great deal has been learned about this very difficult problem and much of it is of use in the process industries where there are frequent occurrences of lower temperature applications which, whilst less demanding, are nonetheless beyond the range of conventional technology. The extensive research programmes which have been conducted in this area, mainly in the US, are critically reviewed. The lessons learned concerning the application of cyclones, electrostatic precipitators, wet dedusters and especially filters are summarised.
This report deals with the determination of the concentration and size distribution of airborne dusts, primarily in relation to gas cleaning. Three distinct situations are identified: the sampling and monitoring of particulates in `ducts`, in the `ambient atmosphere` and for health monitoring in the `workplace environment`. Sampling techniques for particle concentration determination are described, with particular attention being given to the sampling from ducts. Consideration is given to topics such as statutory regulations, sampling locations, flow measurement, accuracy, assessment of health risks and standardised techniques. Particle size analysis techniques which involve the collection of a sample of the material are reviewed. Principal consideration is of cascade impactors and a practical guide is given for their use. Techniques are also described for the direct measurement of concentration and/or particle size. Principally these are optical techniques, although consideration is also given to other sensing methods. The report concludes with a summary of the most commonly encountered types of sampling or measurement device, their approximate specification and source of supply.
This part reviews the performance of different optical dust monitors for continuous monitoring of dust emissions from incinerators. Comparisons are given between dust emission rates determined by extractive sampling and those recorded by monitors. The theoretical operation of these devices is also reviewed and conclusions regarding their suitability are drawn.
SPS GC TG001 The Aerodynamic Module (ADM). This is the first of a new style SPS document which aims to review novel developments in the technology, in this case in gas cleaning. The ADM is a development of the traditional Vane or Louvre dry inertial separator, claiming to achieve efficiency which is better than traditional devices, possibly comparable with a cyclone yet with lower pressure drop.
Volume GC X Part 9 Troubleshooting.
Sections of this manual part will include :-
- Particulate Gas Problems
- Equipment Failure Modes
- Recommended Procedures