| 301. |
- Mocholí Montañés, Rubén, 1990, et al.
(författare)
-
Demonstrating load-change transient performance of a commercial-scale natural gas combined cycle power plant with post-combustion CO2 capture
- 2017
-
Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 63, s. 158-174
-
Tidskriftsartikel (refereegranskat)abstract
- The present work aims to study the transient performance of a commercial-scale natural gas combined cycle (NGCC) power plant with post-combustion CO2 capture (PCC) system via linked dynamic process simulation models. The simulations represent real-like operation of the integrated plant during load change transient events with closed-loop controllers. The focus of the study was the dynamic interaction between the power plant and the PCC unit, and the performance evaluation of decentralized control structures. A 613 MW three-pressure reheat NGCC with PCC using aqueous MEA was designed, including PCC process scale-up. Detailed dynamic process models of the power plant and the post-combustion unit were developed, and their validity was deemed sufficient for the purpose of application. Dynamic simulations of three gas turbine load-change ramp rates (2%/min, 5%/min and 10%/min) showed that the total stabilization times of the power plant's main process variables are shorter (10–30 min) than for the PCC unit (1–4 h). A dynamic interaction between the NGCC and the PCC unit is found in the steam extraction to feed the reboiler duty of the PCC unit. The transient performance of five decentralized PCC plant control structures under load change was analyzed. When controlling the CO2 capture rate, the power plant performs in a more efficient manner at steady-state part load; however, the PCC unit experiences longer stabilization times of the main process variables during load changes, compared with control structures without CO2 capture rate being controlled. Control of L/G ratio of the absorber columns leads to similar part load steady-state performance and significantly faster stabilization times of the power plant and PCC unit's main process variables. It is concluded that adding the PCC unit to the NGCC does not significantly affect the practical load-following capability of the integrated plant in a day-ahead power market, but selection of a suitable control structure is required for efficient operation of the process under steady-state and transient conditions.
|
|
| 302. |
- Mocholí Montañés, Rubén, 1990, et al.
(författare)
-
Large-scale Torrefaction of waste wood for pulverized-coal substitution in blast furnaces: Torero project
- 2018
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of the Torero project is to be the world-first large scale implementation of the waste wood torrefaction for substitution of pulverized coal in blast furnaces. Steel making is highly dependent on coal for reduction of the iron ore in the blast furnace and for energy supply. Substitution of coal with biomass could effectively reduce CO2 emission in steelmaking. However, the steel making process has strict constrains on the properties of the fuel, making it difficult to use a heterogeneous fuel like biomass. In addition, the price of biomass, especially in a carbon constrained energy system, is higher than for coal. The Torero-project considers substitution of the pulverized coal used in the blast furnace with torrefied waste wood. The torrefaction process produces a bio-coal that is possible to mill and use in the present blast burners. Although waste wood is considered as a difficult, due to the high content of contaminants, which limits the alternative uses and, thus, makes it cost-effective in processes where it can be used. The process will be implemented at the ArcelorMittal site in Gent (Belgium), together with the sister project Steelanol, for microbiological fermentation of the carbon monoxide in blast furnace exhaust fumes to bioethanol. The combination of the two projects aims to convert waste wood to produce 80 million litres per year of bioethanol. This work is a first assessment of the Torero project concept. Process simulations are performed in Aspen Plus to evaluate the heat and mass balances of the integrated torrefaction process. The reaction mechanism of the torrefication process of the waste wood are based on small scale experiments and implemented into the reactor model. The ArcelorMittal plant in Ghent is used as a reference in the evaluation. The results of this investigation highlight performance, emissions and technical barriers including the effects of fuel properties and presence of trace species in the fuel.
|
|
| 303. |
|
|
| 304. |
- Nevalainen, H., et al.
(författare)
-
Firing of coal and biomass and their mixtures in 50 kW and 12 MW circulating fluidized beds - Phenomenon study and comparison of scales
- 2007
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 86:14, s. 2043-2051
-
Tidskriftsartikel (refereegranskat)abstract
- The combustion dynamics of coal, wood chips and their mixture is investigated. Load change capability and the effect of the individual control variables, for example the mixture ratio of different fuels, on pilot-scale CFB boiler dynamics were also studied. Disturbances in fuel feeding cause fluctuations in the flue gas concentrations. Changes in the heating value are possible due to varying moisture content of the fuel. Both these disturbances affect the instantaneous firing rate in a boiler. Also the characteristics of the fuels have to be taken into consideration when designing boiler control systems. When co-firing two fuels with clearly distinct combustion characteristics, direct assumptions based on each fuel's characteristies cannot be made about combustion behaviour of their mixture. Combustion experiments with coal and wood chips and their co-firing were carried out in a pilot-scale CFB reactor (VTT) and a large-scale CFB boiler (Chalmers). A comparison of the combustion in the two different size reactors, provides information about scaling. The combustion responses due to changes in the fuel feeding of the two circulating fluidized beds are analyzed by a dynamic model. (c) 2007 Elsevier Ltd. All rights reserved.
|
|
| 305. |
- Niklasson, Fredrik, 1972, et al.
(författare)
-
Biomas co-firing in a CFB boiler
- 2006
-
Ingår i: Proceedings of the 19th FBC Conference. ; 1
-
Konferensbidrag (refereegranskat)abstract
- The aim of present paper is to investigate the effects on gas distribution in a CFB furnace fromburning varied fractions of wood fuel with coal as a base fuel. The work is based on in-situmeasurements of gas concentrations at different locations in the furnace of the Chalmers12 MWth CFB boiler. The boiler was operated at two different pressure drops over the furnace,corresponding to different amounts of bed material. The latter was done since a reducedpressure drop over the furnace improves the overall boiler efficiency as long as the combustionperformance can be maintained. The gas-concentration measurements in the furnace arecompared to results from experiments in a cold laboratory scale fluidized bed unit in which therates of mixing of solids (fuel particles) are determined at varied bed heights and gas velocitiesby frame-by-frame digital image analysis of video recordings. Thus, the gas distribution in thefurnace is assumed to be related to the mixing of fuel particles.The cold bed experiments show a pronounced reduction in solids-mixing rate when lowering thebottom bed height. Since an increased fraction of wood in the fuel mixture leads to a largeramount of volatile gases emitted in the bottom region, a combination of a low bed height and ahigh biomass fraction in the fuel could result in significant maldistribution of combustible gasesover the furnace cross section. The conclusion from the present boiler measurements is that theperformance of an existing CFB boiler, operated satisfactorily with a low furnace pressure dropwhen firing coal, may deteriorate when adding wood to the fuel mixture due to lateralmaldistribution of combustible gases. The results show that this effect can, to some extent becounteracted by increasing the amount of bed material in the furnace, at the cost of higherpressure-drop losses.
|
|
| 306. |
|
|
| 307. |
|
|
| 308. |
- Niklasson, Fredrik, 1968, et al.
(författare)
-
Estimation of the temperature in the bottom region of a fluidized-bed furnace burning biomass
- 2006
-
Ingår i: Science in Thermal and Chemical Biomass Conversion. - 1872691978
-
Konferensbidrag (refereegranskat)abstract
- The heat and mass balance of the bottom region of a fluidized bed boiler burning biomass is established with the aim of determining the furnace temperature. The influence on the temperature by the flow of solids in the upper part of the bottom region is investigated. Heat and mass balances of gas and fuel were applied over a control volume containing the bottom region, i.e. both the bed and the adjacent splash zone. The mass balance is based on given input flow rates of gas and fuel and concentrations in the gas leaving the control volume. The measured gas concentrations were used to determine the rate of fuel burnout inside the control volume. Pressure drop measurements along the height of the furnace estimate the solids concentration. Experiments were performed in a furnace with a cross-section area of 2.2 m2. The walls of the furnace are refractory lined up to a height of 2 m and, for simplicity, the control volume is chosen from the air distributor up to this height. Two fuel mixtures were used: one biomass and one of biomass and coal. The results show that the gas temperature at the top of the control volume strongly depends on the flow-rate of fine particles present in the fluid, even when the volume fraction of particles is small. The particles carry heat to the freeboard, where they transfer heat to the walls before returning to the bottom region. This process has previously been neglected in models of fluidized-bed combustion under bubbling conditions, overestimating the fluid temperature.
|
|
| 309. |
|
|
| 310. |
|
|
