DOWNSCALE APPLICATION OF BOILER THERMAL CALCULATION APPROACH

Commonly used thermal calculation methods are intended primarily for large scale boilers. Hot water small scale boilers, which are commonly used for home heating have many specifics, that distinguish them from large scale boilers especially steam boilers. This paper is focused on application of thermal calculation procedure that is designed for large scale boilers, on a small scale boiler for biomass combustion of load capacity 25 kW. Special issue solved here is influence of formation of deposits on heat exchanging surfaces on efficiency of heat transfer and on overall boiler efficiency. In the paper are presented results of mathematical model created for this purpose and its verification by experimental measurement in this specific boiler

Experimental Investigation of Radial Gas Dispersion Coefficients in a Fluidized Bed

In a fluidized bed boiler, the combustion efficiency, the NOX formation rate, flue gas desulphurization and fluidized bed heat transfer are all ruled by the gas distribution. In this investigation, the tracer gas method is used for evaluating the radial gas dispersion coefficient. CO2 is used as a tracer gas, and the experiment is carried out in a bubbling fluidized bed cold model. Ceramic balls are used as the bed material. The effect of gas velocity, radial position and bed height is investigated

Research and development of CO2 Capture and Storage Technologies in Fossil Fuel Power Plants

This paper presents the results of a research project on the suitability of post-combustion CCS technology in the Czech Republic. It describes the ammonia CO2 separation method and its advantages and disadvantages. The paper evaluates its impact on the recent technology of a 250 MWe lignite coal fired power plant. The main result is a decrease in electric efficiency by 11 percentage points, a decrease in net electricity production by 62 MWe, and an increase in the amount of waste water. In addition, more consumables are needed

NOx PREDICTION FOR FBC BOILERS USING EMPIRICAL MODELS

Reliable prediction of NOx emissions can provide useful information for boiler design and fuel selection. Recently used kinetic prediction models for FBC boilers are overly complex and require large computing capacity. Even so, there are many uncertainties in the case of FBC boilers. An empirical modeling approach for NOx prediction has been used exclusively for PCC boilers. No reference is available for modifying this method for FBC conditions. This paper presents possible advantages of empirical modeling based prediction of NOx emissions for FBC boilers, together with a discussion of its limitations. Empirical models are reviewed, and are applied to operation data from FBC boilers used for combusting Czech lignite coal or coal-biomass mixtures. Modifications to the model are proposed in accordance with theoretical knowledge and prediction accuracy

NOx EMISSIONS FROM BUBBLING FLUIDIZED BED COMBUSTION OF LIGNITE COAL

This paper presents experimental results of NOx emission measurements for combustion of two kinds of coal in a bubbling fluidized bed combustor. The tested fuels were Czech brown coal (CBC) and German young brown coal (GYC). These fuels have different nitrogen contents. The experiments were performed in the pilot scale BFB experimental unit with power output of 500 kW. The influence of several parameters on NOx formation are investigated in this paper. The parameters studied here include the effect of the nitrogen content in the fuel, the effect of the oxygen concentration in the bed, the effect of bed temperature, the effect of air staging, and the effect of fluidization velocity. Significantly different behaviour of the fuels was found. Although GYC has a lower nitrogen content than CBC, it is more reactive and produces higher NOx emissions. The biggest dependence of NOx production for CBC was found for the effects of air staging and fluidization velocity. As the fluidization velocity increases and the amount of secondary air decreases, there is an increase in NOx emissions. The oxygen concentration in the bed has the strongest effect on the NOx production of GYCs. With increasing oxygen concentration, the production of NOx also increases. On the basis of the NOx measurements, the N-NO conversion factor was calculated and the effect of the operating parameters on this conversion factor was investigated

Biomechanics of fixation of proximal femur

V této bakalářské práci je řešena problematika způsobů ošetřování fraktur stehenní kosti, konkrétně fraktur nacházejících se v proximální části femuru. Je zde uvedeno několik způsobů jejich ošetřování, jako jsou dlahy, nitrodřeňové hřeby, fixační pásky a také zevní fixace. Dále jsou zde představeny základní anatomické pojmy včetně stavby dlouhých kostí. Kromě toho je v této bakalářské práci uveden výpočet silového zatížení femuru. Dle vypočteného silového zatížení byl sestaven výpočtový model pomocí metody konečných prvků ve výpočtovém programu Ansys. Model je vytvářen na krátkém rekonstrukčním hřebu.In this bachelor thesis, issues of treating fractures of femur are solved, especially fractures of proximal parts of femur. Several ways of treatment, for example plates, intramedullary nails, fixing cable and external fixation are described here.Basic anatomical terms, including construction of long bones are also presented. There is a calculation of a strength load of femur. According to the calculated strength load, a computional model of final elements with a program called Ansys was completed. The model is created with a short reconstruction nail.

SPECIFIC EMISSIONS FROM BIOMASS COMBUSTION

This paper deals with determining the specific emissions from the combustion of two kinds of biomass fuels in a small-scale boiler. The tested fuels were pellets made of wood and pellets made of rape plant straw. In order to evaluate the specific emissions, several combustion experiments were carried out using a commercial 25 kW pellet-fired boiler. The specific emissions of CO, SO2 and NOx were evaluated in relation to a unit of burned fuel, a unit of calorific value and a unit of produced heat. The specific emissions were compared with some data acquired from the reference literature, with relatively different results. The differences depend mainly on the procedure used for determining the values, and references provide no information about this. Although some of our experimental results may fit with one of the reference sources, they do not fit with the other. The reliability of the references is therefore disputable

Optimal Combustion Conditions for a Small-scale Biomass Boiler

This paper reports on an attempt to achieve maximum efficiency and lowest possible emissions for a small-scale biomass boiler. This aim can be attained only by changing the control algorithm of the boiler, and in this way not raising the acquisition costs for the boiler. This paper describes the experimental facility, the problems that arose while establishing the facility, and how we have dealt with them. The focus is on discontinuities arising after periodic grate sweeping, and on finding the parameters of the PID control loops. Alongside these methods, which need a lambda probe signal for proper functionality, we inroduce another method, which is able to intercept the optimal combustion working point without the need to use a lambda sensor

INFLUENCE OF AIR DISTRIBUTOR ON FLOW FIELD IN FREEBOARD AREA IN A BUBBLING FLUIDIZED BED BOILER

One of the basic functions of the air distributor is to provide uniform fluidization and homogenous flow field above the bed. Thus demand of CFD simulation arises from needs to understand behaviour of the fluidized bed. Situation in this case is complicated by the trough-shaped air distributor. The paper deals with 2D CFD simulations of fluidized bed and confronts it with experimental measurements on pilot scale unit. Simulations and measurements are done under ambient conditions without combustion. Simplified geometry was built up in Gambit and CFD simulations are done by ANSYS FLUENT