Renewable Energy Systems

Transcription

1 Renewable Energy Systems 9 Buchla, Kissell, Floyd

2 Chapter Outline Biomass Technologies THE CARBON CYCLE 9-2 BIOMASS SOURCES 9-3 BIOFUELS: ETHANOL 9-4 BIOFUELS: BIODIESEL AND GREEN DIESEL 9-5 BIOFUELS FROM ALGAE 9-6 ANAEROBIC DIGESTION 9-7 BIOMASS COMBINED HEAT AND POWER Buchla, Kissell, Floyd

3 designua/fotolia 9-1 The Carbon Cycle Biomass is organic material that uses energy from the sun to convert carbon dioxide and water into carbohydrates in a process called photosynthesis. The photosynthesis process can expressed in a chemical reaction as Sunlight + 6CO 2 + H 2 O 6O 2 + C 6 H 12 O 6

4 PHB.cz/Fotolia 9-1 The Carbon Cycle The carbon cycle is the process of circulating carbon in the biosphere. Carbon moves into the atmosphere from several sources. Some major sources are: Natural events, such as volcanic eruptions, natural decay, and wildfires Respiration of living organisms, which includes cellular respiration Man-made sources from burning fuels and burning forests for clearing

5 Dudarev Mikhail/Fotolia 9-1 The Carbon Cycle The ocean is part of the carbon reservoir and also exchanges CO 2 with the atmosphere, however much more is absorbed by the oceans than is released. This has resulted in increases in acidification of the world s oceans and is doing serious damage to corals and shellfish as well as the lowest level of the food chain.

6 Source: NREL 9-2 Biomass Sources Biomass feedstock is any raw material used to create an energy product. Principle sources and examples are: Forest biomass: logging operations, tree trimming Sewage biomass: waste water treatment plants Agricultural biomass: crop residues and fuel crops including algae. Animal biomass: Manure, slaughterhouses, etc. Trash biomass: methane gas, combustible trash Industrial biomass: wood residue and pulp

7 Source: NREL 9-2 Biomass Sources Biomass energy processes include Combustion Burning for heat or steam Co-firing Adding biomass to coal to reduce its amount Thermal conversion Gasification Pyrolysis (charcoal) Torrefaction (briquettes or pellets) Chemical conversion

8 9-3 Biofuels: Ethanol Ethanol is a type of alcohol that is made by fermentation of sugar derived from various plants, mainly grain crops like corn. Ethanol yield is measured by the fossil fuel replacement ratio (FER ratio). FER Cellulosic ethanol Corn ethanol Gasoline Electricity from coal

9 9-3 Biofuels: Ethanol The PRR is the petroleum replacement ratio and is a measure of the energy delivered to the consumer in the form of biofuel to the petroleum energy used in the process. PRR Cellulosic ethanol Corn ethanol Gasoline

10 Source: NREL 9-3 Biofuels: Ethanol Dry milling process: Grinder Convert to coarse flour or meal Slurry and Saccharification Cooker (using high temperatures) Enzymes added Fermentation Add yeast Conversion to ethanol and CO 2. Distillation (separation of ethanol) and dehydration The wet milling process is similar except the first step is to soak the whole kernels in dilute sulfurous acid. Storage

11 Petair/Fotolia 9-3 Biofuels: Ethanol Cellulose-based ethanol production The process of production of ethanol from cellulosic biomass (wood, sawdust, leaves, switchgrass etc.) requires more energy and is more complicated than from starch based resources The National Renewable Energy Laboratory (NREL) is working on the goal of producing cellulosic ethanol that is as cheap as gasoline.

12 9-3 Biofuels: Ethanol The cellulosic ethanol process: Handling Reduce source material to chips, or shreds, etc. Ethanol recovery Lignin utilization Pretreatment Sulfuric acid to break down into simple sugars Cellulose fermentation Pentose fermentation Cellulose hydrolysis

13 9-4 Biofuels: Diesel and Green Fuels Biodiesel process: Acid Esterifcation Transesterification For feedstocks with more than 4% free fatty acids For feedstocks with less than 4% free fatty acids Neutralization neutralizes acid used in previous processes Phase separation Refining and methanol recovery separates biodiesel and glycerin methanol removed and biodiesel purified

14 9-5 Biofuels from Algae Algae are aquatic organisms that use photosynthesis to convert carbon dioxide and sunlight into stored energy. Algae can be used to make various biofuels. Factors affecting growth rates are: Nutrient quantity and quality Light ph Aeration and Mixing Temperature Type of algae

15 9-5 Biofuels from Algae Algae can be grown in large shallow ponds, artificial ponds, tanks, or raceway ponds. Algae can also be cultivated in a photobioreactor (PBR), which is a bioreactor that incorporates a light source. The PBR process is: Incubation Separation Drying Centrifuge

16 9-6 Anaerobic Digestion Anaerobic digestion is the conversion of biodegradable material in the absence of oxygen. Microbes break down the waste into biogas and compost. Waste includes sewage waste, animal manure, and food waste.

17 9-6 Anaerobic Digestion Three steps in digestion: Plant or animal waste decomposes Broken down product is converted to organic acids Acids are converted to methane

18 dioch/shutterstock loraks/fotolia 9-6 Anaerobic Digestion Types of Digesters Batch digester: Waste is digested in batches, and remaining material is removed after days. Continuous digester: Waste is digested continuously in a process that allows new waste to replace digested waste.

19 9-6 Anaerobic Digestion Landfills A landfill is a structure in which trash is isolated from the environment. They are a major source of methane gas through anaerobic digestion.

20 9-7 Biomass Combined Heat and Power CHP systems use combustion or gasification to produce electricity and heat. Three approaches are: Thermal oil Often used in Organic Rankine Cycle (ORC) to generate electricity. Steam Biomass may be combusted for industrial process heat, electrical generation or district heat. Gasification Biomass is combined with an oxidizer to produce syngas.

21 9-7 Biomass Combined Heat and Power A simplified diagram of a CHP plant:

22 Selected Key Terms Algae Anaerobic digestion Carbon cycle Carbon reservoir Combined heat and power (CHP) Any of various aquatic, photosynthetic organisms that range in size from single cell organisms to giant kelp. A bacterial fermentation process in which microorganisms breakdown biodegradable material in the absence of oxygen. The process by which carbon atoms are endlessly cycled around the biosphere A natural feature that stores carbon. A process characterized by the production of both electrical power and heat.

23 Selected Key Terms Ethanol Fossil energy replacement (FER) ratio Photosynthesis Respiration An alcohol made by fermentation of sugars from corn, wheat, rice, sugar beets, sugar cane, sorghum, potatoes, and other starchy food sources as well as cellulosic biomass. The ratio of the energy delivered to the consumer to the fossil energy used at the production site. A process in plants, algae, and some species of bacteria that uses energy from the sun to convert carbon dioxide and water into carbohydrate which is stored in the plant for food. The process in which oxygen is used to break down organic compounds into carbon dioxide (CO 2 ) and water (H 2 O).

24 true/false quiz 1. Photosynthesis mainly stores energy in the form of carbohydrates.

25 true/false quiz 2. When CO 2 is absorbed in the ocean, the result is increased acidity.

26 true/false quiz 3. Algae is a form of biomass.

27 true/false quiz 4. Grains such as corn are sources of cellulosic ethanol.

28 true/false quiz 5. The first step in a starch-based ethanol plant using grain is fermentation of the grain.

29 true/false quiz 6. Cellusoic ethanol can be prepared in fewer steps and for less cost than starch-based ethanol.

30 true/false quiz 7. Anaerobic digestion refers to conversion of biodegradable material in the absence of oxygen.

31 true/false quiz 8. Landfills are a source of ethanol.

32 true/false quiz 9. The Organic Rankine Cycle uses steam to drive a turbine to produce electricity.

33 true/false quiz 10. A form of biogas is syngas.

34 true/false quiz Answers: 1.T 2.T 3.T 4.F 5.F 6.F 7.T 8.F 9.F 10. T