Mini Project Report

On

Production of Syngas from Biomass and Its

Purification

Submitted to:

Muhammad Asif Akhtar

Submitted by:

Muhammad Awais Yaqoob 2011-CH-32

Rizwan Liaquat 2011.CH-72

Nanad Lal 2011-CH-146

―In the name of ALLAH

The most Gracious the most Merciful‖

ABSTRACT

An application for biomass is the synthesis of liquid fuels such as dimethyl ether, and methanol

etc. our effort is intended to explore the syngas production technology from biomass using catalytic

gasification process and the various process and technologies involved in the purification of biomass

derived syngas. In this context, the characteristic of syngas such as yield, the H2/CO ratio and the

different factors affecting H2/CO ration have been studied. This ratio is an important parameter which has

an upper effect on our process. The reactors employ are fluidized bed, gasifier and the fixed bed reactor.

H2/CO ratio lies between 1.87 & 4.45. Further, text of this report involves the purification of syngas.

Three technologies are there for syngas cleanup and are classified according to the temperature of the gas

which is leaving clean up device. The Hot Gas Cleanup technology has been discussed in details because

of energy efficiency and prevention of reheating and cooling of the gas. Wet scrubbers cyclones,

absorbers‘ with varying sorbents are discussed regarding Hot Gas Clean up with new approaches for

Chlorine and Tar removal.

iv

TABLE OF CONTENTS

Table of contents…………………………………………………………………… iv

List of TABELS………………………………………………………………………. vi

1. INTRODUCTION

1.1. Motivation of the project 1

1.2. Chemical Structure 1

1.3. Basic Chemistry 2

1.4. Background & Objective 3

1.5. Scope of the Project 3

1.6. Application and Uses 4

2. FEASIBILITY STUDY AND MARKET ASSESSMENT 5

2.1. Availability of Raw Materials 6

2.2. Market Assessment 6

2.3. Worldwide Production 6

2.4. Regional and National Production 7

2.5. Current and Future Prices 7

2.6. Demand 8

2.7. Import and Exports 8

2.8. Plant Capacity 8

3. LITERATURE SURVEY 10

3.1. Comparison of Different Routes for Syngas Production From Biomass 11

3.2. Effect of varying Temperature and Weight hourly space velocity (WHSV) on

Syngas production 12

3.2.1. Effect of Temperature 12

3.2.2. Effect of WHSV 13

3.3. Description of contaminants present in syngas

3.3.1. Particulate matter 13

3.3.2. Tar 14

3.3.3. Sulphur 14

3.3.4. Nitrogen compounds 16

3.3.5. Chlorine 16

4. PROCESS SELECTION, DESCRIPTION & EQUIPMENT LIST 17

4.1. Production Of Syngas Using Gasification Techniques 18

4.1.1. Process Selection 18

4.1.2. Process Description 18

4.2. Purification Of Syngas 21

4.2.1. Hot gas cleanup technology 22

4.2.1.1. Removal of particulate matter by HGS 23

4.2.1.1.1. Inertial Separation 23

4.2.1.1.2. Removal of Tar 24

4.2.1.1.3. Catalytic Cracking 25

v

4.3. Sulphur Removal 26

4.4. Nitrogen Removal 26

4.5. Alkali Removal 27

4.6. Chlorine Removal 27

4.7. Equipment list 28

5. ENVIRONMENTAL CONSIDERATIONS 30

6. THE PIPING AND INSTRUMENTATION DEAGRAOM OF EQUIPMENT 32

7. CONCLUSION & RECOMMENDATIONS 34

8. REFERENCE 35-36

Page VI

LIST OF FIGURES & TABLES

Table #1 Chemical structure of syngas 1

Table # 2 The Effect of Reaction Temperature on the Performance of the Bio-Oil Steam 2

Reforming Reaction and Dry Gas Composition of the Bio-Oil-Syngas over Three Various Catalysts

Fig # 3 Biomass production & consumption 7

Fig # 4 Supply VS Demand of feedstock through 2030 8

Table # 5 data needed to support a 5MW plant 9

Table # 6 Comparison for different routes for bio-syngas production 13

Table # 7 Experimental results of different fixed bed temperatures at the condition of run no.1 14

Table # 8 Summary of hot gas particulate clean up technology 28

INTRODUCTION

Page 1

CHAPTER # 1

INTRODUCTION

INTRODUCTION

Page 1

1.1 Motivation of the Project

To reduce the greenhouse emits ions of the gases and to establish new and secure energy

sources, various technologies have been developed. Biomass is one of the renewable and secure

energy sources. This report explains the gasification technology to obtain syngas from biomass.

This study is favorable and applicable to a void range of biomass feedstock including rice straw, wheat

straw and grass and is applicable for large scale production. This may be helpful to compensate the

energy crises for Pakistan which currently relies on imported material and lack of energy. This project has

been studied to decide for the optimization of the parameters which may increase the H2/CO ratio in the

syngas and reduce the energy requirement and usage of cheap and more effective catalyst for the

production of syngas.

The gasification of biomass has been studied at the elevated temperature and the syngas produced

by this method acts as the best raw materials for the purification process using hot gas clean up

technology and hence is more energy efficient because the cost of cooling and reheating of syngas have

been minimized. Syngas obtained by gasification process contains impurities such as chlorine, Sulphur,

nitrogen, ash, and especially tar contaminants. In this project hot gas clean up technology over the cool

gas cleanup because cool gas cleanup is energy inefficient. The purity of syngas is important regarding

the environmental considerations and for the safety of equipment‘s and engines operated by syngas and

for the purity of syngas derived biofuels and chemical.

Several cheap and effective catalysts have been under observation and the effect of coking,

temperature increment, deactivation and fragmentation on the catalyst together with tolerant and

regeneration possibilities have been studied so that the best possible and most effective catalyst may be

choose for the efficient and selective removal for the S, N, HCl, and alkali metals may be obtain.

1.2 Chemical Structure

In syngas, although the total hydrogen content of natural gas is high, the amount of free

hydrogen is low. Because of this characteristic, natural gas is not as easy to burn as some manufactured

gases with their high free hydrogen content. The high hydrogen content of natural gas results in more

water vapor produced in the combustion gases with a correspondingly lower efficiency [1,2].

Table #1 Chemical structure of syngas

Composition Coal-Gas Bio-Gas Naturat-Gas

Hydrogen 14.0% 18.0% ---

CO 27.0% 24.0% ---

CO2 4.5% 6.0% ---

O2 0.6% 0.4% ---

CH4 3.0% 3.0% 90.0%

N2 50.9% 48.6% 5.0%

C2H6 --- --- 5.0%

INTRODUCTION

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1.3 Basic Chemistry

To investigate the features of the bio-oil-syngas, we performed the catalytic steam reforming of

the bio-oil over three different catalysts, that is, Mg-doped catalyst, Ni-based catalyst, and Pt.-based

catalyst [3]. Steam reforming of the bio-oil can be simplified as the catalytic steam reforming of the

oxygenated organic compound (CnHmOk) by the following reaction:

CnHmOk + (n-k) H20 → nCO + (n + m/2 – k)H2 (1)

The above reaction is followed by this reaction

nCO + NH2O → nCO2 + nH2 (2)

So the overall process is

CnHmOk + (2n-k) H20 → nCO2 + (2n + m/2 – k)H2 (3)

The most important parameters for the steam reforming of bio-oil are the reforming temperature

(T), the molar ratio of steam to carbon fed (S/C), and the reforming catalysts.

Table # 2

The Effect of Reaction Temperature on the Performance of the Bio-Oil Steam Reforming Reaction and

Dry Gas Composition of the Bio-Oil-Syngas over Three Various Catalysts

Table # 2 shows the effects of the reforming temperature on the hydrogen yield, the carbon conversion

(moles of carbon in gas-phase products to moles of carbon fed), and dry gas composition (i.e., H2, CO,

CO2,CH4) over three different reforming catalysts (i.e., C12A7/15%Mg, 12%Ni/ç-Al2O3, and 1%Pt/ç-

Al2O3).

INTRODUCTION

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1.4 Background & Objective

Self-sufficiency in energy is the assurance to excel any country‘s economy. According to an

international analysis, the oil and gas reserves will be finished into the second half of this current century.

For that reason, to attain self-sufficiency, alternative energy resources are being explored. There are 929

billion tons approx. coal reserves available in the world whose 40% is used to produce the electricity. As

per an estimation, third biggest coal reserve of 185 billion ton exists in Pakistan which is equivalent to

400 billion barrels of oil. In other words, our coal reserves are equivalent to Saudi Arab and Iran‘s

combined oil reserves. Since these natural resources will be finished by end of this century-according to a

survey- so we will have to find other resources which may meet the needs of the future.

Furthermore, pollution may muddy landscapes, poison soils and waterways, or kill plants and

animals. Humans are also regularly harmed by

pollution. Long-term exposure to air pollution, for

example, can lead to chronic respiratory disease,

lung cancer and other diseases. Toxic chemicals

that accumulate in top predators can make some

species unsafe to eat. More than one billion

people lack access to clean water and 2.4 billion

don‘t have adequate sanitation, putting them at

risk of contracting deadly diseases. Keeping in

view of all the above mentioned problems,

researches have been developed regarding the

renewable energy resources which are more

economical, environmental friendly and

renewable.

Renewable energy resources results in

Reduced Pollution

Stable Supply

Environmental Policies

Regional Development

1.5 Scope of the Project

Pakistan is planning to boost exploitation of alternative and renewable energy sources in an

attempt to tackle a chronic power shortage and address the challenges of climate change. A new long-

term energy policy aims to provide at least five percent of the country‘s total commercial energy supplies

from clean renewable sources such as wind, solar and bio-waste by 2030. Demand for energy is

increasing with Pakistan‘s rapidly growing population. The country currently produces fewer than 14,000

MW domestically, a shortfall of 5,000 MW compared to overall domestic and commercial needs. So

according to Pakistani culture, it is very obvious that we have to pay attention to our biomass process.

INTRODUCTION

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1.6 Application and Uses

Syngas is used to produce a wide range of synthetic products i.e. solvents, clothes, and fuels

It is used in the production of methanol which is the origin of hundreds of products including glue

as well.

The hydrogen obtained from acetic acid & formaldehyde is used as a fuel for spacecraft rockets

because H2 provides high energy content per weight of unit.

Fertilizers also have their origin in syngas.

H2 obtained from syngas is used in the production of NH3 and hydrogen itself is used in

the refinery to extract gasoline and more diesel from crude oil

Hydrogen made from syngas is promoted as the energy carrier of the future. Today it is

used as fuel for spacecraft launch rockets where high energy content per weight unit is

valuable and fuel cost a minor.

Made from syngas: Glue is one of hundreds of products with its origin in methanol.

Feasibility of Raw Material and Market Assessment

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CHAPTER # 2

FEASIBILITY STUDY

AND

MARKET ASSESSMENT

Feasibility of Raw Material and Market Assessment

Page 6

2.1 Availability Of Raw Material

Biomass is present in large amount here in Pakistan. 55000 tons of solid waste is generated by

urban area of Pakistan, 225000 tones in the form of crop residue, and almost 1million ton of animal

wastage. Almost 35 million ton of biomass is produced only in Punjab and most of it goes unused. Main

contributors of this biomass are rice straw, bagasse, cotton waste, maize stalks, and husk. Sugar mills

produce around 30-32 million tons of bagasse each year during sugar cane season. From which 30,000 is

sold and rest is use for the purpose of electricity generation. [6]

2.2 Market Assessment

Our main product is syngas which is used in many forms. Wide range of solvent, synthetic

materials, fertilizers & fuels has their origin in syngas. Some of the examples are given below [7-9].

Methanol becomes fuels, adhesive and plastic

Methanol is one of the most important chemicals in world and it is produced in the

amount of 40 million tons per year. It is used as feedstock for formaldehyde, propylene,

polyesters, and formaldehyde production.

Ammonia becomes nylon clothes & fertilizer

We all know that ammonia has a pungent smell but we should know that most of the

foods that we eat in our daily life may be secondary form of ammonia. Moreover it is the

basic need for most of the fertilizers.

hydrogen- a fuel of the future

It is the lightest and most abundantly present molecule in the nature. Hydrogen made

from syngas production is further used in ammonia production, in refinery industry to

obtain more diesel and gasoline from oil.

Moreover it could be used in gas engines.

It is also used as an intermediate in the production of synthetic petroleum

2.3 Worldwide Production

We know that fossil fuels are the primarily source of energy consumption all over the world.

Certainly biomass is very interesting but it is also a very controversial option. [10] It is estimated that

biomass consumption will reach about 1 million tons by 2021, because industry

Feasibility of Raw Material and Market Assessment

Page 7

Fig # 3

expansion heavily depends on biomass production.

2.4 Regional & National Production

Biomass is present in large amount here in Pakistan. 55000 tons of solid waste is generated by

urban area of Pakistan, 225000 tones in the form of crop residue, and almost 1million ton of animal

wastage. Almost 35 million ton of biomass is produced only in Punjab and most of it goes unused. Main

contributors of this biomass are rice straw, bagasse, cotton waste, maize stalks, and husk. Sugar mills

produce around 30-32 million tons of bagasse each year during sugar cane season. From which 30,000 is

sold and rest is use for the purpose of electricity generation. [6]

2.5 Current & Future Prices

Current prices is 105 $/metric ton and according to a survey it would reach up to 150 $/

metric ton.

Feasibility of Raw Material and Market Assessment

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2.6 Demand

Demand of biomass would get triple by 2030, according to a survey, which is placing

pressure on feedstock- survey by LUX RESEARCH [11].

Fig # 4

The report shows that figure will reach to 3.7 billion MT of biomass needed annually by 2030.

2.7 Imports & Exports

Analyst expects that biomass will meet roughly by 20% of renewable energy resource by 2020.

While many countries seem to be crucial to meet these targets. According to a survey, Pakistan is one of

the countries which have most production of biomass in the form of rice straw, wheat straw, bagasse, and

sugar cane etc. And in future most of the countries seem to buy different materials of the biomass from

Pakistan.

2.8 Plant Capacity

Biomass power plants having capacities b/w 3 MW to 7MW are the most economical provided

control area is large enough [12]. A power plant having a capacity b/w 3-7 MW has efficiency of 20-25%

based on gross generation. At efficiency 25% requirement of energy is 3.6MG/0.25 = 14.4 MJ which is

Feasibility of Raw Material and Market Assessment

Page 9

enough to generate 1kWh electricity. As same amount of Hydrogen, Carbon & oxygen are present in any

type of biomass so on moisture and ash free basis it is 50 % C, 44% Oxygen, and 6% Hydrogen by

weight. The Gross Calorific Value (GCV) is about 20 MJ/kg. Furthermore 3.6 MJ = 1 kWh.In the last,

take biomass you want to combust as fired state and we can calculate how much biomass is needed as

shown in following table.

Table # 5

These figures clearly shows how much data is needed to support a 5MW plant

Literature Survey

Page 10

Chapter # 3

Literature Survey

Literature Survey

Page 11

3.0 Literature survey

At high temperature and pressure with steam and oxygen produces syngas. This syngas has 85% CO, and

hydrogen and small amounts of CO2 and CH4 as well as trace amounts of impurities. Moreover, synthesis

gas is the direct product of GASIFICATION PROCESS. Biomass is favored for the production of

syngas because biomass is a CO2 natural source and widely distributed over the Earth. In order to increase

the H2/CO ratio and to decrease the yield of char, air and steam are used as gasification agents and

catalysts are employed because only air gasification of pure biomass produces syngas with low H2/CO

ratio 1. Furthermore, temperature is an important parameter for controlling the H2/CO ratio. The major

components of a gasification steam are

Fluidized bed gasifier

A biomass feeder

A steam generator

An air compressor

A cyclone

And catalytic fixed bed reactor

3.1 Comparison of different routes for Syngas production from Biomass

The different routes for syngas production are [13]

1) From Biomass derived oil

2) From Biomass derived char

3) From reforming of biomass gasification gas

4) From biomass

If we look at the tableb1, it is obvious that route ‗W‘ produces syngas with maximum H2 content and

hence with highest H2/CO ratio. And if we look at route ‗Y‘ and ‗Z‘ the H2/CO ratio in both the routes is

comparable. Direct biomass catalytic route ‗X‘ produces high H2/CO ratio which is more favorable

process ‗Z‘ produces the more CO2 content than the other three routes which is due to catalytic activity of

the nickel catalysts on the gas shift reaction. However, this can be settled by controlling the operating

conditions and improving the nickel catalyst. Process ‗Z‘ produces syngas in a single step while other

routes need two steps. That is why it is more economically viable and has uses more compact equipment.

Hence, it is concluded that biomass catalytic gasification great potential for syngas production and

economically more viable.

Literature Survey

Page 12

Table # 6

Comparison for different routes for bio-syngas production

Process W [2] X [3] Y [4] Z

Feedstock Biomass derived oil Biomass derived char Derived gas Biomass

Gasifying agent H2 & N2 Steam Air-steam Air-steam

Reforming method _ _ bio-gas _

Use of catalyst NO NO YES NO

H2 33.3 70.0 57.64 52.47

CO 29.0 14.8 36.62 14.82

CO2 4.9 14.1 3.07 29.65

CH4 17.0 1.1 2.38 2.9

Others 15.8 _ _ 0.16

Range of 1.15_2.41 4.0_7.0 1.42_1.57 1.87_4.45

H2/CO

3.2 Effect of varying Temperature and Weight hourly space velocity (WHSV) on

Syngas production

3.2.1 Effect of Temperature

By varying temperature and keep the operating conditions constant, it is observed that H2 content

in the syngas increases with temperature because of the endothermic reaction involved in the production

of H2. Furthermore, increase in temperature decrease the CH4 content because of the steam reforming

reaction. The CO content first decreases, and then increases by increasing the temperature which shows

that reaction A → D occurs simultaneously as

CO + H2O → CO2 + H2 ∆H = 411 KJ/mol

CH4 + H2O → CO + 3H2 ∆H = -206 KJ/mol

C + H2O → CO + H2 ∆H = -131 KJ/mol

C + CO2 → 2CO ∆H = -172 KJ/mol

As a result of temperature effect on H2 and CO, the H2/CO ratio first increase and then it

decreases as temperature is elevated and consequently it reaches a maximum value of 4.45 as the

temperature is at 7500C. That is why temperature is an important parameter for controlling H2/CO ratio.

The H2/CO ratio changes between 3.11 & 4.45 as shown in table 7

Literature Survey

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Table # 7

Experimental results of different fixed bed temperatures at the condition of run no.1

Reactor temp (0C) 650 700 750 800 850

Dry free gas composition

(Vol %)

H2 46.28 49.33 49.65 50.23 52.47

CH4 5.24 4.89 4.37 4.3 2.9

CO 14.89 12.28 11.15 12.3 14.82

CO2 32.16 32.81 34.37 32.56 29.65

C2 1.42 0.69 0.46 0.6 0.16

Gas yield 1.87 2.12 2.15 2.24 2.41

Tar yield 6.43 5.53 4.42 4.29 2.35

3.2.2 Weight Hourly Space Velocity (WHSV)

WHSV is the ratio of the biomass flow rate which is fed to the reactor and the mass of catalyst in

the reactor. The content increases with an increase in residence time while that of CO and CH4 decrease

by doing so. However, the CO2 content changes slightly. It is clear from above that applying catalyst

increases the H2 content more favorably. The ratio of H2/CO increase with increase in residence time and

there exist a maximum value of H2/CO for a particular temperature, for example H2/CO value at 7000C

and 8000C lies b/w 2.11 and 3.32 and 2.78 respectively. The H2/CO ratio is low at 800

0C than at 700

0C

because of the reason of the water gas shift reaction being exothermic which decreases the CO

consumption and transformation rate and hence lowers the H2/CO ratio.

3.3.1 Particulate matter

Particle matters which are emitted from a gasifier are of the range of 1µm to 100µm and its

composition varies depending upon feedstock [14]. Inorganic compounds and gasification of biomass

includes bulk of particulate matter. Inorganic contents consist of alkali metals, silica, alkaline earth

metals, iron and magnesium. While minor amounts of arsenic, selenium, zinc, lead, antimony are also

present.

More than 99% removal of particulate are required in most of the syngas applications, as direct

combustion process requires particulate reduction up to 50 mg m-3

. While removing these particulates

fouling, corrosion and erosion are common issues which directly affect its efficiency.

Literature Survey

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3.3.2 Tars

Tars are actually mixture of condensable organic compounds. Tares vary from oxygenated

products to heavy deoxygenated hydrocarbons & polycyclic aromatic compounds [15]. Mostly

thermochemical species produces hundred to thousand tar species according to operating

parameters. Mostly important are feed stock composition & process conditions, especially

temperature, type of oxidant, pressure, amount of oxidant, feedstock residence time [16]. For

example, gasification of wood results in higher tar concentrations having higher amounts of

stable aromatics in comparison to peat or coal. An updraft gasifier works in a different way from

a downdraft gasifier and may yield a product having a composition of 10% - 20%, while the

latter one may yield less than 1% tar.

Tar has complex nature and it creates difficulties in analyzing, collecting, and even

defining what raw material should make tar. A recent effort has defined clear definition of tar

―all the hydrocarbons which have molecular weights higher than benzene‖.

3.3.3 Sulphur

They mostly occur as hydrogen sulfide having small amount of carbonyl sulfide. Sulphur

contaminants in concentration may range from 0.1 Ml L-1

to 30 Ml L-1

. Biomass has less Sulphur

amount than coal. It contains only 0.1 g/kg to 0.5 g/kg Sulphur compared to 50 g/kg as obtained

from coal. Sulphur compounds may corrode to metal surface. If syngas is supposed to burned,

Sulphur is oxidized to Sulphur dioxide which is a regulated pollutant. Even its small amount can

poison catalyst which is used for cleaning process of syngas. In order to avoid these effects, often

removal in parts per billion is required [17]. More than 30 technologies have been formed to

remove Sulphur compounds including CO2

Literature Survey

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. Recent hot gas removal research is focused which uses dry sorbents. These various approaches

have been described in the following fig.

Literature Survey

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3.3.4 Nitrogen compounds

They usually occur as ammonia and hydrogen cyanide. Pyrolysis stage and combustion usually

release nitrogen from protein or heterocyclic aromatic compounds. Amount of released ammonia and

HCN depend on intrinsic properties i.e. N content, physical properties and process conditions. Ammonia

is pure form of nitrogen and it can be formed directly from biomass and from HCN using secondary gas

phase reactions.

3.3.5 Chlorine

Chlorides are usually present in syngas in the form of hydrochloric acid (HCL). In biomass they

usually occur as alkali metal salts and they vaporize in a temperature of high environment, polarizers or

gasifier and react with water vapor and result in the formation of HCL. Raw syngas may contain several

millimeters of chloride per liter of syngas. Although it has lower concentration as compared to other

contaminants yet it can cause many of the problems to the material. If chlorine level is low as 20 µL/L it

will affect nickel anodes % solid oxide fuel cells.

Process Selection, Description and Equipment list

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CHAPTER # 4

PROCESS SELECTION, DESCRIPTION AND EQUIPMENT LIST

Process Selection, Description and Equipment list

Page 18

4.1 Production Of Syngas Using Gasification Techniques

4.1.1 Process Selection

There are several routes for conversion of agricultural biomass to useful products and energy. The

well-known process are

Fermentation

Pyrolysis

Gasification

Above all three processes, gasification process is the most favorable because of the high conversion of

biomass and its utilization for useful products. Using this method above 90% of biomass is converted to

the desired products or energy. That‘s why we selected this process.

4.1.2 Process Description

The thermochemical gasification process includes the following major events as described in

PFD.

Process Selection, Description and Equipment list

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The biomass (grass, wheat straw, rice straw) is firstly pulverized to fine particles. This is done in

a pulverizer where the feed is grinded. The biomass here contains water (moisture). That’s why

it is necessarily dried. The biomass is dried at high temperature of 300° C. in a non-oxidant

environment and for an effective residence time. This means a semi batch drier is used . This results in

at least about 90 wt. % removal of the moisture from biomass and hence biomass feed and a first vapor

phase gas stream is produced.

The next approach is to convert this biomass to the syngas by gasification process. The mehots widely

used is from GTI Gasifier. Gasifier works at high pressure (3.45 MPa) and includes a high

temperature of about 800 to 900° C. This gasifier requires superheated steam for the required heat

effect. The reaction takes place in presence of oxygen.

Process Selection, Description and Equipment list

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Cross sectional area at the lower part is smaller than that of at the upper part of the gasifier.

This design is effective and results in a high gas velocity zone at the bottom part of the gasifier,

preventing large particles from falling to the bottom while allowing only the defined small

particles to move upward along the gas flow due to the low gas velocity at the upper zone.

Despite the unequel particle size distribution of the grinned biomass, unreacted large particles

and raw material that require relatively large reaction times are kept inside the gasifier until the

reaction achieves the pseudu steady state is achieved, thus having high carbon conversion

efficiency which is chiefly required.

The oxygen flow of oxygen and steam required for this process is 0.3 and 0.4 kg/kg of dry

biomass (grass, wheat straw, rice straw etc.) respectively. The biomass size is effective in this

fluidized bed reactor. This fluidized bed reactor is highly efficient as compared to the fixed bed

reaction with respect to its efficiency. The efficiency depends upon the particle size.

Process Selection, Description and Equipment list

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The reaction produces syngas which contains some contaminants like chlorides, sulfides and

alkalis. The ash formed is recovered from the bottom of the gasifier. The hot gasses with

product gases and char are transferred to the cyclone. Char is separated from the bottom. The

remaining solid contaminants are removed from the syngas by the scrubber. The detailed

purification process of the syngas is described in the next section.

4.2 Purification Of Syngas

The cleaning technology for syngas purification has been classified as

Cool gas cleanup technology ( T < ~1000C )

Hot gas cleanup technology ( T > 3000C)

Warm gas cleanup technology

Cool gas cleanup technology is less favored due to energy inefficiencies and hot gas cleanup technology

is favored over cool & warm technology because they avoid the reheating and the cooling of the gas

streams.

Process Selection, Description and Equipment list

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4.2.1 Hot gas cleanup technology

The cleanup method employed for the cleaning of syngas depends on the end use of the syngas

.Hot gas cleanup technology focuses on the removal of tar and particulate matter with the aim of

minimizing the maintenance of the equipment which is derived by the syngas. The benefits of hot gas

cleanup have decreased waste streams, increased efficiencies and improved syngas conversion with least

Process Selection, Description and Equipment list

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4.2.1.1 Removal of particulate matter by HGS

The technique applied to hot gas cleanup are based on the principles of inertial separation,

electrostatic interaction based on biomass separation.

(a) Inertial separation

Inertial separation devices work on the principle of mass acceleration to separate higher gases

from heavier solids. The most efficient device in this context is cyclone but alternative devices are also

available like impact separators and agglomerates. Operating conditions for cyclone are in excess of

10000C and these are one of the most commonly employed and oldest means of solid separation. Cyclone

work on the principle of centripetal force and use centripetal acceleration to decrease the long time

needed otherwise for the small particles to settle down by gravity. The syngas stream enters at the ―double

vortex‖ that initially forces the particulate outward and then downward in an outer vortex. This outer

swirling caused by the outer vortex separates the vapors from the particulate matter initial forces. Finally,

through a vortex the syngas stream is redirected into an upward moving vortex before the syngas exits the

device. Depending on the nature and characteristics of the particle and of the syngas, the cyclones are

designed.

Process Selection, Description and Equipment list

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A point is established, typically called

as ―Cut point‖ where a balance is obtained by

certain sized particle b/w the drag force and the

centrifugal force. At this point the particle size

is cut size and it has a 50% removal efficiency

represented as x50 or d50. For example, a cyclone

which is designed for x50 of 10µm shows that a

10 µm particle has a chance of 50% to get

removed. Smaller particles are removed more

efficiently given the smaller centrifugal force

compared to drag force and vice versa is true

for larger particles. The lack of moving part

and simple designs of cyclones make them

efficient for high temperature syngas cleanup

but has only the limitations of the mechanical

strength of the construction materials. They are

operated at high temperature, so that

condensation of water, tar and other

contaminants doesn‘t occur which may foul the cyclone. Cyclones are the first cleanup devices applied to

the cleaning of syngas streams and up to 90% of the particulate matter which may be small up to 5 µm

can be efficiently removed by cyclones which sometimes require more multiple stages.

(b) Removal of tar

The basic approaches for removing tar from syngas are

Thermal cracking

Catalytic cracking

Non-thermal cracking

Physical separation

Although, the equilibrium predicts chemical that there are no tarry compounds in the product syngas but

actually there is always tarry (condensable organic compound) in the gas obtained as a product. The

content of tar compound decreases as the temp increases. However, if the gasification chemical

equilibrium is obtained, tar is not expected to be present at relatively moderate temperatures. Catalytic

cracking, thermal cracking and non-thermal cracking intend to more closely approach to the equilibrium

by increasing the decomposition rates of the tar. On the other hand, physical separation of tars cools the

gas to condense the vapors into liquids and these liquids are removed by physical means.

The above mentioned methods are employed in both primary and secondary tar removal environments

depending of the intended application of the syngas and the type of gasifier. Gasifier using catalytic and

thermal cracking may achieve tar concentration up to 50 mg/m3 which is applicable to direct combustion

Process Selection, Description and Equipment list

Page 25

of the syngas. For the application of syngas to the catalytic conversion increases and fuel cell, the

secondary methods of tar cleanup are used these methods can remove tar up to un-detectable levels.

(b) Catalytic Cracking

It occurs at the lower temperature than the thermal cracking and occurs when the activation

energy for decomposing the tar compound is reduced. This process is more efficient because it has the

efficiency to lower costs which are associated with the high temperature clean up. In this process catalysts

may face the problems of poisoning carbon decomposition of fragmentation which can be reduced by

modifying the catalyst compositions. Modification of the catalyst can be effective by increasing the

durability of the catalyst or by interring the reaction rats of the catalysts.

The extreme conditions encountered during the regeneration of the catalyst can be tolerated by

increasing the attrition resistance i.e. durability of the catalyst. The hot gas clean involves high

temperature which results in catalyst sintering which again can be tolerated by increasing the durability.

Catalyst involved in the tar cracking can be classified

Based on the chemical mechanism which involves basic, iron based, nickel based and acid

catalyst.

Catalyst based on the temperature conditions and cheapness which involves limestone and

dolomite

The catalyst based on the essential design parameters which involves chemical elements on

which the catalyst is based, the parameter of the catalyst and the surface area.

The catalyst based on their origin which is mineral or synthetic

The approach based on the origin of the catalyst will be used in this text because it is both

comprehensive and simple. Origin based catalyst may be mineral based on synthetics. Mineral based

catalyst are solids of homogeneous nature, and have variable but distinct compositions. These catalysts

can be altered physically but can be altered chemically. These catalysts are generally less expensive and

include such materials as calcinated rocks, clay minerals, olivine, and porous metal oxides. On the other

hand, synthetic catalysts are expensive as compared to mineral based catalysts because of the

requirements of the chemical treatments.

These include metal based ( Fe, Or, Ni based ) catalysts, activated alumina, alkali metals carbonates,

FCC catalyst and char. Minerals are low cost and abundant and mineral based calcinated rocks are mostly

employed for tar removal. Dolomites are common examples of mineral based catalysts and the have the

efficiency of more than 95% tar conversions. The tar decompositions is particularly more effective using

Ni than using mineral based catalyst. The activity of Ni-based catalyst is 3-10 times more than of mineral

based catalyst, such as dolomites tends to increase the H2 level by 0.06 L/L to 0.11 L/L (on dry syngas

basis).Ni catalyst are fouled by coking and poisoned by H2S due to this reason reforming of the catalyst is

also necessary

Process Selection, Description and Equipment list

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4.3 Sulphur Removal

Sulphur removal focuses on the removal

SO2

H2O

At high temperatures, mostly HGC technologies use adsorption where gaseous species combine

chemically or physically with the solid materials. Adsorption occurs either irreversible or reversibly.

Reversible processes are favored for expensive synthetic materials and allow for the sorbents regeneration

if the adsorbed contaminants are to be permanently removed from the gas, the irreversible adsorption is

favored.

Adsorption material include metal oxides and combination of metals as Mn mixed with Cu and

‗v‘ have high Sulphur removed capacities at temperature just above 6000C. Zn and Cu oxides have

removal efficiencies that exceed 99% combination of metals used as adsorbents such as Zn ferrites have

better efficiency and regeneration properties e.g. the fresh Zn ferrite catalyst was employed, it will have a

high Sulphur removed capacity of more than 300g/kg.

Doping is another technique in which ZnO and other sorbents with CuO to ensure low Sulphur

concentrations and more prominent for first stage removal of Sulphur. Other combinations with CuO

involve Al2O3 and Fe2O3. The equilibrium b/w this and CuO enhances the adsorption of Sulphur and

increased the performance. Addressing to the different flow issues and mass transfer, the sorbent

geometry is of great importance and it includes a variety of forms of size such as tablets or extrusions or

granuales. To reduce the waste streams and material inputs the regeneration of metal sorbents is important

biomass derived syngas has varying amounts of chlorides, nitrogen and alkali contaminates and the affect

the catalyst life time and make the regeneration step more difficult.

4.4 Nitrogen Removal

HGC focuses on the removal of nitrogen compounds by decomposition of ammonia rather than

removing ammonia from gas streams. If the chemical equilibrium was attained, there should be very little

ammonia. Oxidation of gas streams which contains ammonia leads to the destruction of NH3 into H2 & N2

and NO. Selective oxidation approach is employed that minimized the severity of conditions for the

decomposition of NH3. Catalyst use for selective oxidation of nitrogen compounds thereby avoiding undesired

species. NO is a promising oxidizing agent. However Ni and zeolites are also used in thermal catalytic

decompositions.

4NH3 + 6NO → 5N2 + 6H2O

5H2 + 2NO → 2NH3 + 2H2O

Process Selection, Description and Equipment list

Page 27

4.5 Alkali Removal

At elevated temp, two process are commonly used to reduce alkali concentrations

Removal via condensations with other contaminants

Hot adsorption onto the solid adsorbants

A sorbent generally termed as ―getter‖ is selected using the following utilities

It should tolerate high temperature

It must possess a high adsorption rate

Irreversible adsorptions sorbents life time is dependent on the application temp, the presence of other

contaminants and the regeneration ability of the sorbent. Sorbents include the natural minerals i.e. silicon,

kaolinite or clays. They can also be synthesized from minerals. Minerals such as bauxite and kaolinite are

capable of removed application at the elevated tamp. Some sorbents like SiO2 and Al2O3 based minerals

are able to remove both chlorine and alkali from gas at temp approaching 8000C

4.6 Chlorine Removal

Chlorine is mostly found in biomass and because of the ability of chloride salts to form under

certain condition, a substantial portion of the chlorine evolves as HCl. In Hot Gas Cleanup a sorbent is

employed that remove HCl only and sometimes also the alkali metals. Due to the establishment of the

equilibrium b/w solids and the gases involved, the HCl removed is more efficient b/w 500-5500C. On the

industrial scale alumina, carbon and common alkali oxides are employed in fixed beds.

Table # 8

Summary of hot gas particulate clean up technology

Process Selection, Description and Equipment list

Page 28

4.7 Equipment list

Pulverizer

Gasifier

Cyclone

Dryer

Compressor

Heat exchanger

Scrubber

catalytic Reformer

Tar reformer

Fluidized bed reactor

Steam generator

Feed tank

Adsorber

Pump

Environmental Considerations

Page 29

CHAPTER # 5

ENVIRONMENTAL CONSIDERATIONS

Environmental Considerations

Page 30

6.1 Environmental Considerations

Sources of biomass resources for producing electricity are diverse, including energy crops (like

switch grass), agricultural waste, manure, forest products and waste, and urban waste. Both the type of

feedstock and the manner in which it is developed and harvested significantly affect land use and life-

cycle global warming emissions impacts of producing power from biomass.

Biomass fuels "recycle" atmospheric carbon, minimizing global warming impacts since zero

"net" carbon dioxide is emitted during biomass combustion, i.e. the amount of carbon dioxide emitted is

equal to the amount absorbed from the atmosphere during the biomass growth phase.

There are global warming emissions associated with growing and harvesting biomass feedstock,

transporting feedstock to the power plant, and burning or gasifying the feedstock. Transportation and

combustion emissions are roughly equivalent for all types of biomass. It was once commonly thought that

biomass had net zero global warming emissions, because the growing biomass absorbed an equal amount

of carbon as the amount released through combustion. It is now understood that some biomass feedstock

sources are associated with substantial global warming emissions.

Burning biomass to produce electricity can impact air quality. The level of air emissions associated with

biomass power plants varies depending on the feedstock, combustion technology, and types of installed

pollution controls, but the most common pollutants include nitrogen oxides (NOx), sulfur dioxide (SO2),

carbon monoxide, and particulate matter. The table below compares air emissions from different types of

biomass, coal, and natural gas power facilities with pollution

Approximately 75% of existing biomass plants that require cooling use wet-recirculating

technology, while 25% of plants use once-through cooling technology. In either case, when withdrawn

cooling water is returned to its source, it is much warmer than when it was withdrawn, which often has a

negative impact on plant and animal life. As in all thermal plants, this impact must be closely monitored.

Dry-cooling systems do not withdraw or consume any water, but the tradeoffs to these water savings are

higher costs and lower efficiencies—meaning more fuel is needed per unit of electricity.

The Piping and Instrumentation Diagram

Page 31

CHAPTER # 6

THE PIPING AND INSTRUMENTATION DIAGRAM ON ONE OF EQUIPMENT

The Piping and Instrumentation Diagram

Page 32

Conclusion & Recomendations

Page 33

CHAPTER # 7

CONCLUSION

&

RECOMENDATIONS

Conclusion & Recomendations

Page 34

Conclusion and Recommendations

Syngas has many applications, ranging process heat and power to chemical and fuels synthesis.

Gasifying contaminated feedstock to syngas offers an opportunity to transform otherwise polluting

combustion fuels or idle waste into relatively useful materials. Gasified biomass is a versatile supplement

to a primarily fossil-based energy infrastructure, and provides an alternative renewable source of

chemicals and fuels for a growing populace. Raw syngas unfortunately contains contaminants derived

from the thermochemical process or impurities in the feedstock that cause problems during use. Syngas

must therefore be relatively purified of the contaminants, specifically particulate matter, tar, H 2S, NH3,

alkali formations, halides and trace contaminants. There are numerous processes available to provide a

relatively clean H2 and CO syngas stream. These technologies can be roughly classified into three

regimes according to their operational temperature: hot gas cleanup (HGC), cold gas cleanup (CGC), and

warm gas cleanup (WGC). HGC has received the greatest attention in the recent past, especially in the

removal of tars, particulate matter, and sulfur. Several mature technologies have existed for decades to

remove particulate matter, including cyclones, electrostatic precipitators, and barrier filtration. The

complex tars that are created in gasification reactions are typically reduced to lighter compounds by

thermal and catalytic methods. Thermal techniques experience some losses and inefficiencies when

raising the temperature by partially combusting the syngas stream. Most research has therefore focused on

overcoming the coking, deactivation and economic challenges associated with catalytic methods for use at

slightly lower temperatures. Removing sulfur at high temperatures is primarily done with adsorption onto

a variety of solid sorbents. These methods may provide gains in thermal efficiency, process simplicity and

the potential for cost reduction using generable sorbents, but overcoming activity losses and increasing

sorbent lifetime remains challenging.

References

Page 35

REFERENCES

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