SCRUBBER ABSORBER NEWSLETTER
January 2005
No. 367Miniature Scrubber Can Predict Both Particle Removal and Absorption Efficiency
With new ambient fine particulate rules, plants will be forced to make reductions. In many cases there are other regulations which will also require reduction of mercury, HCl and SO2. It is therefore critical to determine the multi-pollutant capabilities of proposed scrubbers. Due to the concentration of acid mist deposits from scrubbing it is essential to address the condensibles problem prior to scrubber installation.
The science of mercury speciation and prediction of mercury capture in SO2 scrubbers is very poor. Yet it is critical to determine the mercury capture which will be achieved with installation of scrubbers. SO2 scrubbers are already designated to play the most important role in mercury reduction.
The typical response from system suppliers when asked about particulate and mercury guarantees is the following:
(1) We will provide a particulate guarantee based on a particle size distribution supplied to us. But if the emission target is not met and we do our own particle size analysis later and find that the distribution has changed, then our guarantee is void. The guarantee only applies to discrete particulate and not condensibles. We may be able to give some weak guarantee on SO3 removal.
(2) We will provide a qualified guarantee on mercury removal based only on the oxidized mercury and not on elemental mercury.
The reality is that the purchaser who proceeds based on the above type guarantees is no better off than with no guarantees. It is disappointing that 30 years after McIlvaine alerted the industry to the risks, it is still relying on particle size distributions.
Particle size distributions are highly inaccurate (not reproducible) and even if they were accurate, they do not directly indicate the particulate removal ability of a scrubber. All they indicate is the ability of impingement plates to capture particles at varying velocities. The density, particle shape and electrical characteristics are as important as the mythical particle diameter of a non-spherical particle.
The only sure way to determine the weight reduction of particulate of the scrubber is to install it and measure the results. But if you need the information now, then the next best way is to install a miniature scrubber which approximates the performance of a full-scale scrubber.
The mercury removal ability of the scrubber depends on a number of variables. This art (not science) is in its infancy. Again the only way to determine how much mercury will be removed by an SO2 scrubber is to install one. So the best way to determine performance in advance is to install a miniature scrubber and test its performance.
SO3 and other condensibles capture in the scrubber are very complex. The operation of a miniature scrubber and measurement of upstream versus downstream condensibles would add greatly to the decision making process.
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