Gravimetric coal dust firing and dry lignite firing in power plants

Gravimetric coal dust firing and dry lignite firing in power plants

1 POWER PLANTS: Gravimetric dosing and transport technology for coal dust firing and dry lignite firing Currently, a significant share of electricity generation is still produced in coal power plants (i.e. 45% of total generation in Germany). Coal fired power plants can be distinguished on the basis of coal used: hard coal or lignite. The power plant is designed accordingly. Before the coal is burned, raw coal is milled and ground for these energy producing processes. The burning of the coal is the core process which produces thermal energy which, after being transferred into a water-turbine-generator-cycle, ultimately generates the electricity. It is huge amounts of coal dust which is therefore airflown into the up to 1,200 degrees Celsius hot boilers. In modern generating units up to 500 tons per hour are typical. Fig. 1: Gravimetric belt weighfeeders Pfister GBF also come in individual special sizes

2 The quality of this burning process and therefore the heat generation is significantly influenced by the injection of an exact and constant amount of fuel per time unit. There it becomes apparent which important role an exact dosing of the fuel plays. When it comes to dosing fuels process technology distinguishes between volumetric and gravimetric dosing. Volumetric systems like trough chain conveyors, belt conveyors or disk conveyors dose material volume-based; gravimetric systems like Pfister rotor weighfeeders weigh the material and therefore dose it mass-based. The latter, a constant mass flow, is decisive for the regularity of the burning process. A regular burning process then again results in higher efficiency in operating a generating unit. Fig. 2: Energetic value of the transported fuel as a function of dosing technology (gravimetric vs. volumetric) Why does gravimetric dosing of coal dusts in power plants outplay volumetric dosing? In volumetric dosing the material discharge refers to volume or quantity. Not measured is the mass (= weight) of the fuel. Also, possible variations in humidity or density of the bulk material are not included in the measurement. In gravimetric dosing however, integrated load cells measure the weight of the bulk material to be dosed. Thus, potential deviations in bulk density are recorded and compensated by an automatic set-actual comparison. That way a mass-related discharge of the respective fuel and thus an extraction basing on the same calorific value per time unit, is secured. The German industrial dosing experts of FLSmidth Pfister are specialized on gravimetric systems for fuels like bulk material. They have solutions in their portfolio which are especially employed in coal power plants. Flexible application of gravimetric systems Gravimetric belt feeders Pfister GBF, for example, are mechatronically far advanced systems which support operators of power plants in an economic firing of the boiler. In comparison to volumetric dosing equipment the gravimetric belt feeder Pfister GBF operates with a higher accuracy with regard to the extracted energetic value. While the accuracy of volumetric dosing units technologically gets impaired by changing parameters like material density, energetic value or size of the pieces, the gravimetric belt weighfeeder Pfister GBF is able to compensate these impacts as far as possible. This leads to a considerably higher accuracy in terms of energetic value of the transported fuel as figure 2 illustrates. In coal power plants often times material silos with broader outlets are employed, this is why FLSmidth Pfister also engineered special versions of the gravimetric belt weighfeeder Pfister GBF which adapt to this prerequisite (fig. 1). Depending on the spatial circumstances often times a plug and play subsitution of old volumetric systems with modern gravimetric dosing systems is possible. Fig. 3: Gravimetric belt feeder Pfister GBF in a coal power plant

3 Latest technology: Gravimetric dosing with rotor weighfeeders Even further advanced gravimetric dosing One technical step further in terms of fuel dosing for direct boiler firing go the also gravimetrically operating rotor weighfeeders Pfister TRW-K. They are, inter alia, employed to substitute technologically aged dosing systems. Rotor weighfeeders base on a slowly revolting, horizontal rotor. For dosing, crushed coal is extracted from a material silo and transported in the rotating wheel (2) from the inlet to the outlet. The rotor corpus is mounted on weighing cells which form a weighing axis (A-A). The axis is eccentric to the middle of the rotor and goes through the middle of inlet and outlet. The third support point is suspended at a weighing cell (1) which weighs the content of the rotor gravimetrically. This means, the rotor weighfeeder measures the actual weight and is thus a real scale. The measured value provides information on the coal mass in the rotor weighfeeder before material discharge. The material content of the rotor weighfeeder with the related rotor position is stored by the feeding dosing controller Pfister. The required speed of the rotor for the time of the discharge is electronically calculated and controlled invers to the measured value F. Thus the rotor weighfeeder discharges the material at the outlet (3) in a constant mass flow: This is the prerequisite to ensure a constant and consistant burning process in the boiler. Proactive control of the dosing process State-of-the-art Pfister dosing electronics calculate the necessary speed of the rotor in relation to the moment of material discharge. It relates to the preset feed rate and the measured bulk material mass to calculate the angular frequency of the rotor. Less material load in the rotor leads to a higher angular frequency, more material results in a lower angular frequency of the rotor. With this proactive principle, the prospective dosing control ProsCon, the Pfister rotor weighfeeders manage a high-precision compensation if deviations in rotor load and/or material density occur. This results in a decidedly precise short- and long-term feed rate, explains Antonio Rizzo, coal power plant expert at FLSmidth Pfister. Plasma torches for more flexibility Since renewable energy sources like wind and sun are more intensely used in Germany, coal power plants are no longer working at full load. However, the amount of energy gained by renewable sources might fluctuate considerably daily, even hourly. These are situations when conventional power plants have to react most flexible to the current demand. Older power plant are exclusively calculated to work at full load. Their ability for flexible operation is very limited. More modern power plants are already designed for flexible deliv- A A 2 Fig. 4: Technical principle of gravimetric dosing with Pfister rotor weighfeeders 3

4 New technology: Dry lignite to substitute petroleum in starting-up a generating unit ery of electricity. Momentarily, power plants are testing plasma torches which are fired with dry lignite. On the one hand this fuel is used instead of petroleum to start-up the boiler, on the other hand it is employed for reasons of more flexible operation of the boiler. The objective is to design lignite-fired power plants in a way that these show a similar performance flexibility as petroleum and gas-fired power stations, explains Antonio Rizzo. So one can react better to the increasing input of electricity from regenerative sources. Flexible operation Rotor weighfeeders Pfister DRW support this flexibility insofar as these shock pressure resistant dosing systems are especially made for dosing pulverized fuels. The dry lignite is stored after milling until its using. The fuel is then extracted from this intermediary bin into a calibration bin which is placed above the rotor weighfeeder. From there the pulverized dry lignite literally falls into the horizontal rotor inside the rotor weighfeeder Pfister DRW. The slowly revolving rotor transports the fuel from the inlet to the outlet. During this weighing takes place in combination with the above already described adaption of the rotor speed. The integrated pneumatic transport leads to a constant gravimetric fuel discharge. The system is laid out completely closed, dust-tight and shock pressure resistant. Fig. 6: Rotor weighfeeders Pfister DRW employed for dry lignite firing Fig. 5: Rotor weighfeeder Pfister TRW-S is designed to dose varying alternative fuels and bio masses with one and the same system Alternative fuels Pfister systems are also able to dose alternative fuels and biomass into a boiler firing process. For this purpose rotor weighfeeder Pfister TRW-S/D was especially designed. It can be employed for dosing of alternating as well as mixed secondary fuels. The special challenge in dosing secondary fuels lies in their ever changing humidity and bulk density. A pre-bin, mounted above the rotor weighfeeder Pfister TRW-S, is equipped with a particular agitator which prevents a jamming of the materials in this stage and secures a continuous material stream into the rotor weighfeeder. Due to the particular arrangement of the cells of the rotor in combination with the state-of-the-art weighing electronics materials with different densities and sizes can also be weighed exactly and thus discharged into a constant material stream.

5 Application of rotor weighfeeder Pfister URW in flue gas cleaning In the area of flue gas cleaning rotor weighfeeders Pfister URW are employed. Here, powdered limestone is weighed gravimetrically and pneumatically blown into the flue gas process. Thereby, handling capacities of 5 t/h are realized. Fig. 7: Rotor weighfeeder Pfister URW installed for flue gas cleaning in a power plant That s what the expert says to replacement of volumetric dosing systems with latest gravimetric dosing systems Antonio Rizzo is business development manager and expert for coal power plants at FLSmidth Pfister GmbH/Germany. Modern gravimetric dosing systems have considerable advantages over volumetric systems when it comes to dosing fuels in power plants. Why are these gravimetric solutions not already used by every operator? Antonio Rizzo: The conversion of an existing volumetric system to a modern gravimetric one is associated with certain rebuilding costs and additional costs. Some operators are reluctant to invest, and only become active when old systems actually fail or government regulations are issued. The latter is, for example, the case in India. In order to improve the collection and control of emission values, the government would like to take a closer look at the consumption of raw coal. So they demand more precise consumption data, which can be achieved by using gravimetric systems. Why should plant operators nevertheless consider this investment? Antonio Rizzo: The use of gravimetric dosing systems instead of volumetric systems pays off in the medium-term. Gravimetric feeding of the boiler is more stable, the dosing becomes more constant. This, at the same time, saves fuel costs and has a positive effect on the CO 2 balance of the system and less NO x production. Why are not more rotor weighfeeders employed in coal power plants compared to the number of belt weighfeeders? Antonio Rizzo: For the application of rotor weighfeeders round-coned silos instead of the old square-coned ones should be built. From the construction point of view this would be the much more space-saving solution, but for a plant manufacturer it would initially be a certain additional effort to change his engineering standard. Nevertheless already a considerable number of plant manufacturers responded to this technological solution. Are there other projects for dosing of dry lignite? Antonio Rizzo: Yes, there are further studies on this topic, but the currently very low oil and petroleum prices, especially in Germany, are an obstacle. Furthermore, the issue of coal burning for generating electricity has a rather negative tune in the discussions in Germany. However, there is a clear trend in other European countries to keep on building new coal-fired power plants.

About FLSmidth Pfister GmbH Stable and accurate dosing of fuels and materials is one of the key elements required for efficient and profitable industrial dosing processes. With its state-of-the-art Pfister gravimetric dosing concept, FLSmidth Pfister is offering a future oriented technology for rotor weighfeeders and belt weighfeeder that is able to dose small to huge numbers of tons per hour. With almost 3,000 installations worldwide, customers of FLSmidth Pfister are feeding millions of tons each and every year. See here how Pfister rotor weighfeeders work FLSmidth Pfister GmbH Stätzlinger Str. 70 86165 Augsburg Germany Tel.: +49 821 7949 0 Fax: +49 821 7949 524 E-mail: sales@flsmidthpfister.com Copyright 2014 FLSmidth A/S. ALL RIGHTS RESERVED. FLSmidth, Pfister, ProsCon and all other product names used herein are (registered) trademarks of FLSmidth A/S. This brochure makes no offers, representations or warranties (express or implied), and information and data contained in this brochure are for general reference only and may change at any time. all pictures: J.K Cement and/or FLSmidth A/S www.flsmidthpfister.com CS.003.01-0-GB