Fluidization and gas-solid systems - introduction - AGH

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Fluidization and gas-solid systems - introduction

MSc. Leszek Stepien Faculty of Energy & Fuels

Winter 2014/2015

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 prof. Marek Sciazko

 Monday 9.45-11.15

 OBLIGATORY attendance

LECTURE (30h)

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Expected achievements

 Student is aware of advanced knowledge in the field of the implementation of typical fluidization and

other gas-solid systems, and principles of their design.

 Has advanced knowledge of fluidization process arrangement and specific component’s function, particularly in a high velocity fluidization.

 Is able to use the acquired knowledge to solve

specific engineering problems of fluid bed systems.

MS-AGH-2014 3

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Student’s grading

 Evaluation is a shared responsibility between the teacher and the student. The purpose of the evaluation is to demonstrate how well the student has learned specific course materials, the principles, concepts and terms relevant to the fluidization field, and to determine the students’ ability to apply that knowledge to specific engineering problems.

 Final grade (OK) is calculated as weighted mean of lecture test (T), seminar delivered work (P):

OK = 0,4·w·T + 0,6·P

 w – student’s activity; w=1; attending at least 80% of lectures, w

= 0,7 more than 50% and less than 80%, w = 0,3 for more than 50% unjustified absences.

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 Msc. Leszek Stępień

 Friday 10-11.30

 OBLIGATORY attendance

 Grade: class test + activity/homework (problem solving)

CLASSES (15h)

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1. Fludization velocities

a) Calculating mean diameter of particles b) Minimum fludization velocity

c) Terminal velocity 2. Gas distributors

3. Bubbling fluidization a) Size of bubbles

b) Kuni-Levenspiel bubbling bed model 4. Entrainment & elutriation

5. Fluid bed aerodynamics

6. Application example – drying process

Topics

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Fluidization

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The idea of fludization

 Set of solid particles with of different size

(diameter/mass/density) is lifted by the counter current flow of gas to form the uniformly spread bed

Advantages:

 Uniform temperature distribution

 Large contact area between solid and gas phase

 Good mixing => uniform

concentration of substrates and products in the system

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The idea of fludization

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Flow regimes

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Pros & Cons

 Smooth flow = easier control

 Isothermal conditions

 Good resistance to rapid temperature changes

 Heat and mass transfer

 Suitable for large scale operations

 Difficult to describe flow of gas

 Nonuniform residence time

 Entrainment of friable solids

 Erosion of pipes

 Possible agglomeration

and sintering

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Fluidization significance

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Energy generation

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 Based on the steam parameters:

 subcritical pulverized coal (SubCPC) plants,

 supercritical pulverized coal (SCPC) plants,

 ultra-supercritical pulverized coal (USCPC) plants

 Based on parameters inside the furnace:

 Atmospheric

 Pressurized

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The heart of powert plant - BOILER

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Circulating fluid bed

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 Around 2 million tons of coal will be required each year to produce the continuous power.

 Around 1.6 million cubic meter of air in an hour is delivered by air fans into the furnace.

 The ash produced from this combustion is around 200,000 tons per year.

 The boiler for typical 500 MW units produces around 1600 tons per hour of steam at a temperature of 540 to 600 degrees C. The steam pressures is in the range of 200 bar.

 The steam leaving the turbine is condensed and the water is pumped back for reuse in the boiler. To condense all the steam it will require around 50,000 cubic meter per hour of cooling water to be circulated from lakes, rivers or the sea.

The water is returned to the source with only an increase of 3 to 4 degrees centigrade to prevent any effect to the environment.

 Apart from the cooling water the power plant also requires around 400 cubic meter per day of fresh water for making up the losses in the water steam cycle

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500MW power plant - overview

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 Polands newest & most efficient power plant (44%)

 the world's largest CFB boiler

 High efficiency => lower fuel requirements, and lower levels of ash and emissions, including carbon dioxide (CO2).

 CFB technology has excellent fuel flexibility and

offers the option of co-firing of biofuels with different grades of coals, which can further reduce CO2

emissions.

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Łagisza power plant

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 40-50 kg of coal/sec !!

 Fluid bed approx 300 000kg

 The fuel and limestone particles are recycled over and over back to the process, which results in high

efficiency for burning the fuel, capturing pollutants, and for transferring the fuel's heat energy into high- quality steam to produce power.

 Steam: 27,5 MPa, 560C

 No chimney

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Łagisza power plant

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 Load flexibility and high heat transfer rates

 Fuel flexibility, can gasify a wide range of feedstocks

 Moderate oxidant and steam requirements

 Has a uniform, moderately high temperature throughout the gasifier

 Higher cold gas efficiency than entrained-bed gasifiers, but lower carbon conversion

 Extensive char recycling is required

Fluid bed gasifier

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 The HTW gasifier is a circulating fluidized-bed reactor which operates in either air or oxygen blown modes.

 Dry-feed, pressurized, dry ash gasifier.

 A key advantage of the technology is the capability to

gasify a variety of different feedstocks, including all grades of more reactive low-rank coals with a higher ash softening temperature (i.e., brown coal), and also various forms of biomass.

 Due to the high outlet temperature, the syngas does not contain any higher molecular weight hydrocarbons, such as tars, phenols, and other heavy aromatics.

High Temperature Winkler

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 The bottom part of the gasifier comprises a fluidized-bed (the fluidizing medium air/oxygen +steam)

 The bed is formed by particles of ash, semi-coke and coal, and is

maintained in the fluidized state via upward flow of the gasification

agent

 Gas plus the fluidized solids flow up the reactor, with further air/O2 and steam being added in this

region to complete the gasification process.

 Fine ash particulate and char entrained in the raw syngas are removed in a cyclone and cooled.

 The solids removed in the cyclone are returned to the gasifier base to maximize carbon conversion

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 EU energy in figures 2012

 http://www.pke.pl/

 http://www.elko.com.pl/elkoweb/site2/site.php

 http://www.brighthubengineering.com

 http://www.freund-vector.com/lab/equipment.asp

 R. Szafran et al., New spout-fluid bed apparatus for electrostatic coating of fine particles

 and encapsulation, Powder technology(2012), 225

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Fluidization and gas-solid systems - introduction - AGH