Contents Issue 04 (2017)

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The Influence of Ash Composition on Fouling and Slagging Propensity in a Coal-Fired Power Plant Boiler
Marisa AbadeÇo and Una Nowling

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Coal is a very complex fuel due to its chemical and physical properties. The effects of coal combustion behavior, such as fly ash loss on ignition or slagging and fouling, will affect power plant performance, such as boiler efficiency and possible load deviations. The most common causes for slagging and fouling are a low excess of oxygen, high primary airflows, burner damage, poor coal pulverizer conditions, and coal chemistry. This paper addresses the last point, analyzing the influence of the sodium and iron content in coal on fouling and slagging phenomena in pulverized coal boilers. The formation of eutectic mixtures from the different oxides causes a drop in the fusion temperatures in the boiler convective zone.

PowerPlant Chemistry 2017, 19(4), 187–192
Chemistry Aspects of Industrial Turbines
James C. Bellows

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Industrial turbines appear in a wide variety of applications and under a wide variety of operating conditions.

They may be operating at variable speed, particularly in marine turbines. They may be used as backpressure turbines, where their primary purpose is to reduce high-pressure steam to pressures used in a process, but producing electric power as a byproduct. In this use, the steam may be removed from the turbine in the superheated state and there is no moisture transition. The implications of backpressure are explored.

Another use is for district heating. In this application, turbines have been configured so that a single condenser is shared among multiple turbines. If the steam is not needed, one turbine may be idle over an operating condenser.

Most industrial turbines are not reheat turbines, and the implications of this fact, such as the possibility of on-line washing to remove water soluble deposits, are also explored. The common idea that salts may be more concentrated in steam to non-reheat turbines than in steam to utility turbines is erroneous. Salt concentrations should be the same as for utility turbines. Silica requirements might be a bit higher than for utility turbines.

PowerPlant Chemistry 2017, 19(4), 197–201
Global Experiences in Optimizing Biofouling Control through Pulse-Chlorination®
Maarten C. M. Bruijs, Lars P. Venhuis, and Ludwin Daal

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Cooling water systems provide optimal conditions for the settlement and growth of fouling species, e.g. mussels, oysters and barnacles. Excessive biofouling results in major operational upsets and even unplanned shutdowns. Controlling micro- and macrofouling organisms in once-through cooling water systems is key to safe, reliable operation. For this, chlorination is globally still considered one of the best technology options. Sodium hypochlorite is applied either as bulk-product or is produced on site by means of an electro-chlorination plant. The common industry practice is continuous dosing, often combined with shock dosing.

However, despite this approach many installations still experience significant operational and economic consequences. The likelihood and frequency of operational issues is site specific and in addition may result from increasingly strict permit limits, the need to operate with dwindling (human) resources and settlement of new types of fouling species. Pulse-Chlorination® (PC) is an optimized intermittent dosing procedure, implemented through a science-based assessment procedure on site. It has proven to be highly effective regardless of the geographic location and species of concern. In addition, PC is not only applicable to sodium hypochlorite, but to any biocide that is able to trigger and alter the behavior of the fouling species. In general, the dosing technology reduces the required volumes of hypochlorite up to 50 % compared to continuous dosing, leading to a significant reduction in operational costs and environmental impact, while the mitigating efficacy is high. Motivated by increasingly strict environmental regulations, a focus on operational cost reductions and increased plant availability, installation owners are looking for environmental and cost-saving alternatives.

PC has globally received recognition as a proven technology and is implemented at many industrial sites throughout Europe, the Middle-East, Asia and Australia. The efficacy of the optimized dosing schedule is controlled by in-plant monitoring of biofouling trends and the continuity of the applied dosing regime by strategic monitoring of residual oxidant levels.

PowerPlant Chemistry 2017, 19(4), 203–209
Insights and Lessons Learnt from a Scaling Event in a Cooling Tower Part I: Statement of the Problem and Introduction to the Methodology of the Investigation
Emmanuel K. Quagraine

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This is the first half of a two-part article on a scaling incident that occurred at the Shand Power Station, SaskPower. The event exemplifies scaling as a costly operational problem associated with the reuse of secondary treated municipal effluent when logistical challenges compel operations outside designed limits. The plant, which was commissioned in 1992 and operates on a zero liquid discharge program, has since 1994 been using treated sewage effluent as a significant but variable portion of its cooling tower make-up water. As far as scaling is concerned, apart from the early adjustment periods, the operation had been largely successful, especially in the previous twelve years. Over the summer of 2014, however, due to restricted outlets to manage the blending of the treated sewage effluent with fresh surface water, the plant by its contractual obligation had to take untypically disproportionate amounts of the treated effluent whilst also faced with a series of cooling water treatment equipment breakdowns. This forced cooling tower operations to the water chemistry fringes, where the scaling potential was high; ultimately, fouling of the condenser occurred, resulting in significant electricity generation unit derates. The paper describes the event, the operating conditions, and an assessment of the chemical treatment effectiveness, as well as the mitigation efforts made, including an on-line acid clean to restore the generation unit back to normal load. Several lessons to be learnt from the event are outlined.

PowerPlant Chemistry 2017, 19(4), 213–222
The Fourth Meeting of the European HRSG Forum (EHF 2017)
Ladi Bursik

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The fourth EHF (European Heat Recovery Steam Generator Forum) meeting took place in Amsterdam, the Netherlands, on May 16–18, 2017. The successful format from the first three meetings was followed again – presentations mixed with extended open floor discussions. Around 80 participants from 20 countries (Abu Dhabi, Belgium, China, Czech Republic, France, Germany, Greece, Hungary, Israel, Italy, Ivory Coast, Kingdom of Saudi Arabia, Netherlands, Oman, Spain, Switzerland, Thailand, Tunisia, United Kingdom, and U.S.A.) and four continents participated in the meeting.

PowerPlant Chemistry 2017, 19(4), 223
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Last updated: 24.07.2017