Carpet Waste Gasification:

Technical, Economic, Environmental Assessment for Carpet Mills

ENGR4300

University of Tennessee at Chattanooga

May 6, 2011

Project Team:

Jordan Buecker

Christopher Burns

Katharine Davis

Hemali Dholakia

Kevin O’Brien

Table of Contents

1 Executive Summary 1

2 Introduction 2

3 Process Flow Diagrams and Descriptions 2

3.1 Air Gasifier ..................................................................................................................................... 2

3.2 Oxygen Gasifier ............................................................................................................................. 3

3.3 Steam Gasifier ............................................................................................................................... 4

4 Components 6

4.1 Cyclone Separator ......................................................................................................................... 7

4.2 Gas Turbine ................................................................................................................................... 7

4.2.1 Fuel Conditioning for Gas Turbine ........................................................................................ 7

5 Material Balances 8

6 Environmental Analysis 11

7 Economic Analysis 12

8 Discussion 13

9 Conclusions 13

10 Recommendations 13

11 References 13

1

Executive Summary

2

Introduction

With the cost of fuel ever increasing and the current push towards “going green,” new and

innovative methods must be developed to reclaim and recycle usable energy from previously untapped

resources.

Post-consumer carpet waste (PCC) is carbon based material and can be gasified to produce

syngas. With a heat of combustion similar to coal, syngas enables much usable energy to be reclaimed

from the carpet rather than losing that energy to a landfill.

It is our goal to provide a means for carpet manufactures to reclaim some of the energy in the

carpet that comes back to them for consumer recycle/disposal. The method chosen to accomplish this is

gasification and production of synthesis gas (syngas).

Three main types of gasifiers exist and are explored in this report. The gasifiers explored are: air

gasifier, oxygen gasifier and steam gasifier. Process flow diagrams and descriptions are shown in section

3.

Process Flow Diagrams and Descriptions

Air Gasifier

Figure 1 shows the process flow diagram (PFD) for the air gasifier.

3

Figure 1: PFD for air gasifier

As presented in Figure 3, the air and carpet waste enter the gasifier where they react to produce

syngas and calcium oxide (CaO). The CaO/syngas mixture then enters a cyclone separator where they

are separated. The CaO is stored for later disposal and the syngas is sent to a combustion/boiler unit for

the production of steam.

Oxygen Gasifier

The oxygen gasifier operations identically to the air gasifier except there is need to have nearly

pure oxygen as a reactant rather than air. Figure 2 shows the PFD for an oxygen gasifier.

4

Figure 2: Oxygen gasifier

Steam Gasifier

The steam gasifier uses steam as the reactant with carpet. The syngas produced by this

gasification process contains methane and has a higher heating value than syngas produced by air and

oxygen gasification. Because of the higher heating value, the syngas can be used to power a gas turbine

for production of electricity. Figure 3 shows the PFD for the steam gasifier.

This image cannot currently be displayed.

5

Figure 3: Steam gasifier

Uses for Syngas

Current use

Currently, for PCC, the syngas produced is combusted in a boiler to produce steam for facility

use. Figure 4 shows the current industrial use for carpet manufacturers.

6

Figure 4: Current PPC-produced syngas usage.

As discussed in section 3.3, the syngas can be combusted in a gas turbine to produce work. The

exhaust from the gas turbine can then be captured to produce steam, which will drive a stream turbine.

The steam turbine may be non-condensing or condensing. If it is non-condensing, the steam turbine

exhaust can be used for facility use. Figure 5 shows use of syngas in a gas turbine combined with a

steam turbine.

Figure 5: Use of syngas with gas and steam turbines

Components

7

Components described in Figures 1-5 are described in this section.

Cyclone Separator

Cyclonic separation utilizes a difference in mass between two streams—typically a fluid (air) and

solid. The mixed stream of fluid and particulate enter the separator tangentially and the inertia of the

mass of the particulate causes it to strike the wall of the separator and fall to the bottom. The fluid

stream has sufficiently small inertia and can follow the wall of the separator radially [1]. Figure 4 shows

a typical cyclone separator.

Figure 4: Cyclone separator [1].

The separation efficiency increases with the ratio of length to diameter and with particle size (mass of

particle).

Gas Turbine

Fuel Conditioning for Gas Turbine

Contaminants in the turbine fuel stream can be harmful to the turbine and affect performance.

Fuel conditioning is often required.

Fuel conditioning for use with gas turbines involves removing small particulate matter, excess

water, nitrogen, and other undesired gaseous contaminants. Filtering through an ultra-fine particle or

membrane filter is usually the standard method for fuel conditioning [2]. Because work produced by a

gas turbine is driven by the temperature difference, heating or cooling of the fuel stream may also be a

part of fuel conditioning. Figure 5 shows a possible configuration for a turbine fuel gas conditioning

system. Here, the crude fuel gas enters a preheater/cooler and then splits to go to one of two filters.

After filtration, the streams recombine and go into a second preheater/cooler and then go to the

8

turbine for combustion.

Figure 5: Turbine fuel gas conditioner [2]

Material Balances

The material balances for the gasifiers are modeled assuming the reactions associated with each go to

completion. The oxygen and air gasifiers have five reactions which are assumed to take place, while the

steam gasifier has six. The five general reactions are listed below:

1. PET (polyethylene terephthalate):

2. SBR (Styrene butadiene rubber):

3. N66 (Nylon 6-6):

4. PP (Polyproylene):

5. CaCO3 (Calcium Carbonate):

9

The additional reaction for the steam gasifier is the reaction of the carbon monoxide with the steam

(water) present to produce methane and carbon dioxide.

6. Methane Production: 2��� 2��� → ��� � ���

Although some carbon monoxide (part of the syngas) is used up to produce methane, the syngas which

includes methane has a higher LHV than one containing just CO and H2 in normal amounts.

To accompany these PFDs, Tables 1, 2, and 3 show the material balance for the air, oxygen and steam

gasifiers, respectively. A basis of 10,000 lbs PCC per hour per each of two gasifiers is used. The initial

carpet composition is 35% ash (CaCO3), 12% polypropylene (PP), 11% SBR, and 42% face fiber; the fiber

is composed of 40% N6, 33% N66, 15% PET, and 12% PP [3]. Assuming all N66 and 80% of the ash are

removed prior to gasification, the carpet composition flow rates in the following tables were estimated.

ChemCAD software was used in modeling the gasifiers.

Table 1: Material balance for air gasifier

Carpet Air Post Gasification

Temperature (F) 70 70 1740

Pressure (psia) 14.7 14.7 14.7

Composition Flow

Rates (lb/h)

1,700 PP

700 CaCO3

1,400 N66

630 PET

1100 SBR

4,460 O2

16,800 N2

500 H2

16,900 N2

390 CaO

8,900 CO

HHV (BTU/lb) 1,140

Volumetric Flow

Rate Syn Gas (scfh)

450,000

The carpet and air are mixed and sent to the gasifier at 70 F and 14.7 atm. The temperature of

10

the stream leaving the gasifier is 1740 F. The flow rate of the syn gas including N2 is 450,000 standard

cubic feet per hour.

Table 2: Material balance for oxygen gasifier

Carpet O2 Post Gasification

Temperature (F) 70 70 1830

Pressure (psia) 14.7 14.7 14.7

Composition Flow

Rates (lb/h)

1,700 PP

700 CaCO3

1,400 N66

630 PET

1100 SBR

4,460 O2

500 H2

170 N2

390 CaO

8,900 CO

HHV (BTU/lb) 1,140

Volumetric Flow

Rate Syn Gas (scfh)

221,000

The carpet and O2 are mixed and sent to the gasifier at 70 F and 14.7 atm. The temperature of

the stream leaving the gasifier is 1830 F. The flow rate of the syn gas including N2 is 221,000 standard

cubic feet per hour.

Table 3: Material balance for steam gasifier

Carpet Steam Post Gasification

Temperature (F) 70 212 1080

Pressure (psia) 14.7 14.7 14.7

11

Composition Flow

Rates (lb/h)

1,700 PP

700 CaCO3

1,400 N66

630 PET

1100 SBR

3,850 H2O

630 H2

110 O2

170 N2

390 CaO

6,900 CO

1,200 CH4

HHV (BTU/lb) 3,470

Volumetric Flow

Rate Syn Gas (scfh)

250,000

The carpet and steam are mixed and sent to the gasifier at 212 F and 14.7 atm. The amount of

energy required to heat the steam is 350 MBtu/hr which includes a 10% loss. The temperature of the

stream leaving the gasifier is 1080 F. The flow rate of the syn gas including N2, CH4, and O2 is 250,000

standard cubic feet per hour.

Environmental Analysis

To assess the environmental performance of the three gasification designs, energy production,

water consumption, and pollutant emissions were analyzed. All calculations are based on 4,430 lb

PCCW/hr (10,000 lb PCCW/hr with N6, SBR, and 80% of CaCO3 removed) fed to each of two gasifiers.

Water consumption is only applicable to the steam gasifier which requires 3850 lb H20 (460 gallons) per

hour per gasifier to gasify the 4430 lb PCCW/h. Energy production is based on the composition of the

syngas produced by each gasifier. Using the HHV for each syngas composition and an assumed

efficiency for the energy recovery system, the amount of energy produced is approximated. For the air

and oxygen gasifiers, an efficiency of 25% is assumed for the steam generator; for the steam gasifier, an

efficiency of 40% is assumed for the combined cycle. Energy production estimates are in Table 4.

Possible pollutants are carbon dioxide and nitrogen oxide. Assuming all of the carbon entering the

gasifier is released as CO2, 2700 lb CO2/hr will be emitted per gasifier. Assuming a flame temperature

of 1950C (2223K), nitrogen oxide emissions can be approximated at 180 ppm (see Figure 6). See Table 4

for a summary of these estimations.

Table 4: Water consumption, energy production, and emissions for 20,000 lb PCCW gasification

Gasifier Type Water Consumed Energy Produced

(BTU/hr)

CO2 Emitted NOx Emitted

12

AIR 290

5,400 lb/hr

180 ppm OXYGEN 290

STEAM 920 gal/hr 1390

Figure 1: NOx emission vs. Adiabatic flame temperature (from industrialheating.com)

Economic Analysis

The estimation of capital costs was completed using the module costing technique. This

technique factors in the equipment type, system pressure, and materials of construction as multiples

that adjust base costing conditions. The computer program CAPCOST 2008 was utilized for the

generating the estimates shown below in Table 5. The program generates an estimate using the

parameters entered by the user.

Table 5: Cost estimate

Type Equipment cost Bare Module Cost

Gasifier $688,000 $1,730,000

Cyclone Separator $99,400 $149,000

13

Packaged Steam Boiler $733,000 $1,590,000

Total Bare Module Cost $3,469,000

The estimate in Table 5 is for a gasifier system to produce syngas to be burned for steam

generation. Further use of the steam for electricity generation will be determined later in the design

process.

Discussion

Conclusions

Recommendations

References

1. Cyclonic Separation. Accessed electronically. <http://en.wikipedia.org/wiki/Cyclonic_separation>.

2. EML Manufacturing, LLC. Fuel Gas Conditioning. Accessed electronically.

<http://www.emlmanufacturing.com/Fuel_Gas_Conditioning.htm>.

3. Shaw report

<http://en.wikipedia.org/wiki/Adiabatic_flame_temperature> accessed May 4, 2011

<http://www.industrialheating.com/Articles/Feature_Article/566ce7aa44cb7010VgnVCM100000f932a8

c0____> accessed May 4,2011

<http://en.wikipedia.org/wiki/Heat_of_combustion#Lower_heating_value_for_some_organic_compoun

ds_.28at_15.4.C2.B0C.29> accessed May 4, 2011

“Energy Efficiency & Industrial Boiler Efficiency: An Industry Perspective.”

<http://cibo.org/pubs/whitepaper1.pdf> accessed April 25, 2011

<http://www.naturalgas.org/environment/naturalgas.asp> accessed May 4, 2011