Carpet Waste Gasification:

Transcription

1 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

2 Table of Contents 1 Executive Summary 1 2 Introduction 2 3 Process Flow Diagrams and Descriptions Air Gasifier Oxygen Gasifier Steam Gasifier Components Cyclone Separator Gas Turbine Fuel Conditioning for Gas Turbine Material Balances 8 6 Environmental Analysis 11 7 Economic Analysis 12 8 Discussion 13 9 Conclusions Recommendations References 13

3 Executive Summary 1

4 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. 2

5 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. 3

6 This image cannot currently be displayed. 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. 4

7 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. 5

8 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 6

9 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 7

10 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. CaCO 3 (Calcium Carbonate): 8

11 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 H 2 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) Pressure (psia) Composition Flow Rates (lb/h) 1,700 PP 700 CaCO3 4,460 O2 16,800 N2 500 H2 16,900 N2 1,400 N CaO 630 PET 8,900 CO 1100 SBR 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 9

12 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) Pressure (psia) Composition Flow Rates (lb/h) 1,700 PP 700 CaCO3 1,400 N 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) Pressure (psia)

13 Composition Flow Rates (lb/h) 1,700 PP 700 CaCO3 1,400 N 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 11

14 AIR 290 OXYGEN 290 5,400 lb/hr 180 ppm 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 12

15 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. < 2. EML Manufacturing, LLC. Fuel Gas Conditioning. Accessed electronically. < 3. Shaw report < accessed May 4, 2011 < c0 > accessed May 4,2011 < ds_.28at_15.4.c2.b0c.29> accessed May 4, 2011 Energy Efficiency & Industrial Boiler Efficiency: An Industry Perspective. < accessed April 25, 2011 < accessed May 4,