Abstracts - VGB PowerTech Journal 11/2012

CCP management in Europe

Fernando Caldas-Viera and Hans-Joachim Feuerborn

In Europe (EU 27) more than 100 million tonnes of Coal Combustion Products (CCPs) are produced in coal-fired power stations. CCP management includes safe disposal, storage, and utilisation. Based on trials in some countries, several environmental and technical benefits of by-products ´utilisation have been observed. Meanwhile, the utilisation of CCPs has been well established in some European countries and practised for decades. The utilisation of CCPs in Europe is being influenced by political decisions and environmental regulations.

Solar updraft power technology State and advances of low-concentrated thermal solar power generation

Wilfried B. Krätzig

In the medium term, European energy policy is aiming at low-emission energy supply with solar-based energy playing a main part. Solar updraft power plants are one option, the concept of which is being outlined. A mathematical model of a solar updraft power plant is presented and the resulting simulation program is scaled with a pilot plant. Besides, studies about optimised electricity generation carried out at two plant sizes are presented. The studies demonstrate the concept´s economic efficiency.

CFB - Multi-fuel design features and operating experience

Pekka Lehtonen and Jan Strömdahl

The combustion process of a circulating fluidised bed (CFB) boiler is inherently flexible and enables utilisation of a wide range of fuels. This is well proven especially in industrial power plants. Naturally, the practically applicable fuel range of an individual boiler depends on various facts, including fuel properties and design parameters selected of the plant equipment. The main features of two co-combustion approaches are presented. The first is designed for a limited share of challenging fuels (solid recovered fuel, SRF in 10 to 20 % range), while the main fuels are more conventional (wood-based biomass, coal, peat). The second approach facilitates a fuel range from 100 % SRF to 100 % demolition wood to 100 % coal.

Prediction of slagging and fouling of furnaces and heat exchanger surfaces in boilers by simulation

Günter Scheffknecht, Olaf Lemp, Reinhard Leithner, Martin Strelow, Bernd Epple and Michael Müller

CFD simulation of pulverised coal combustion has obtained increasing relevance as an engineering tool in power plant technology and is successfully used during the design phase of new projects and during optimisation processes of already existing power plants (retrofit). The paper outlines the description and implementation of the relevant mechanisms of fouling and slagging into a CFD code. Three simulations of power plants with different thermal input and operation with different coals are presented.

Investigations on torrefied biomass for the co-combustion in pulverised fired furnaces

Falah Alobaid, Jan-Peter Busch, Jochen Ströhle and Bernd Epple

The torrefaction process is a thermal treatment of raw biomass during the absence of oxygen at a temperature range between 200 to 300 °C and at a residence time of 15 to 90 minutes under atmospheric pressure. Here, the released water and low calorific volatile components reduce the mass by approximately 30 % while the energy content of torrefied biomass decreases by about 10 %. Compared to raw biomass, torrefied biomass is easier to grind and has a high energy density similar to coal. The Institute for Energy Systems and Technology (EST) at the Technische Universität Darmstadt is currently researching the torrefaction process of biomass. The proposed model will be validated towards the measurements in the frame of a CFD simulation program.

Fuel chemistry and tube leakages in biomass-fired boilers

Anja Klarin, Daniel Nordgren and Ilkka Heikkilä

Today, many fluidised bed boilers originally designed for combusting wood residues (bark) are now firing sludge and rejects generated at adjacent pulp and paper mills. Paper mill sludge typically has a high ash content leading to frequent boiler shutdown due to ash deposit problems. The paper discusses measures for analysing fuel, influences on deposit formation, boiler corrosion and possibilities to select a suitable fuel range in order to avoid any negative impacts.

Upgrade of the pulveriser/dryer at the Bexbach power plant

Albrecht Meiser

The 750 MW hard coal-fired power plant was commissioned at the Bexbach site in 1983. The plant was designed for the sole combustion of
local Saarland hard coal. Due to changing general conditions, the plant had to be adjusted to the combustion of world market coal. Upgrading of the pulveriser/dryer was among the measures taken. After checking of several alternatives, it was decided to apply gas surface burners. It was an absolute novelty to employ a pulveriser/dryer in a power plant of that design which gave the project a pilot character. Already when commissioning the new pulverisers, it was realised that the retrofit exceeded expectations.

Indirect firing system to increase flexibility of existing steam cogeneration plants

Torsten Buddenberg, Karl Burmann, Thomas Furth, Alfons Leisse, Roland Jeschke, Georg Papenheim and Ulrich Lohmann

The Hanover power plant is taken as example. The implementation of measures - required due to the changing energy supply situation - are being discussed, i.e. the grid has to be stabilised due to the increasing feed-in of fluctuating renewables-based power. It is shown qualitatively how the plant can be retrofitted to cope with the new situation. In future, controllable power plants will increasingly cover residual electricity demand, i.e. demand to be covered beyond renewables-based power produced and consumed.

Operating behaviour and optimisation of the flue gas channels of an heat recovery steam generator

Rene Hofmann, Thomas Walch, Arno Kolbitsch, Heimo Walter and Christian Daublebsky von Eichhain

The study was aiming at the examination of empirical values for operating- and load change behaviour of a combined cycle power plant. The analysed vertical heat recovery steam generator (HRSG) with top supporting heating surfaces and multi-pressure construction method with natural circulation evaporators is described. The exhaust gas is supplied to a boiler from two Siemens gas turbines SGT-800 with an approximately exhaust mass flow of 132 kg/s each and an exhaust gas temperature of approximately 563 °C (at full load). An inevitable high demand for optimisation of the gas-side is particularly required to ensure an even flow behaviour upstream of the heating surfaces and provide an even heat absorption of the bundle heating surfaces as well as to avoid any flow inclinations. Therefore, the flue-gas channel was numerically optimised between the two gas turbines and the heat recovery steam generator. In the second part of the study, measurement data from a cold start-up process of the HRSG are compared with simulation calculations.

Implementation of single coal mill operation in the Bexbach and Heilbronn (unit 7)  power plants

Timm Heinzel, Albrecht Meiser, Georg-Nikolaus Stamatelopoulos and Peter Buck

In the Bexbach and Heilbronn (unit 7) hard coal-fired power plants, units with an installed capacity of 750 and 800 MWel respectively, the single coal mill/burner level operation was tested and implemented. The firing of an individual burner level is possible without any decrease of the combustion stability and enables thus substantial decrease of the minimum boiler load below the limits of conventional operation with two mills. After implementation of single mill operation, the minimum load is not any more limited by firing constraints, but by other restrictions, mainly of in the steam cycle.

Extending the operating period of lignite-fired boilers

Thomas Endres and Horst Hoffmann

The units of the Neurath power plant are shut down every three years for a scheduled inspection. During these outages, the prescribed in-service inspections and any necessary maintenance work and conversions are performed on the steam generators. In addition to maintenance/refurbishments, monitoring and optimising the day-to-day operation of the plant are also of major importance. For this reason, various plant surveillance and diagnostic tools such as leak monitoring, optical and infrared cameras and a statistical process control system have been installed. Furthermore, a model-based process quality optimisation scheme has been introduced in all units to identify further optimisation potentials. Thanks to these measures, the non-scheduled unavailability (NSUA) has remained under control in recent years despite more stringent demands.

Electrical and I&C systems in German nuclear power plants - Safe and highly available until the end of operating life time

Markus Bresler

The electrical and I&C components of German nuclear power plants often have been in operation for more than 30 years at high availability levels. This has to be maintained for the remaining operating time of the plants according to the 13th amendment of the German Atomic Act.
The resulting challenges are huge: plant availability is more important than ever, facing the end of nuclear production by 2022. The support by vendors consequently declined drastically. Plant operators take the challenge on a solid base: the accumulated operating experiences is rarely found in other branches of industry.

Fly ash in construction for the Moorburg power plant

Rene Herrmann

At the production site Hamburg Moorburg, Vattenfall Europe Generation AG is building a 2 x 820 MW hard coal-fired power plant. For the construction of the power plant different requirements regarding concrete technology have to be considered. The specific requirements can be described by geometrical and climatic requirements as well as production technology. The exposure classes cover internal concrete, WU-constructions as well as wharfs and cooling towers. Nearly all concretes use fly ash as concrete addition, in total more than 15,000 tonnes.