Zerihun Alemayehu (AAiT-CED)

Transcription

1 Zerihun Alemayehu (AAiT-ED) Tools for quantitative understandg of the behavior of environmental systems. For accountg of the flow of energy and materials to and of the environmental systems. 1

2 onservation of Matter 3/29/2011 Material Balance Energy Balance Pollutant Energy modelg production, transport, and fate The law of conservation of matter states that (with nuclear reaction) matter can neither be created nor destroyed. We ought to be able to account for the matter at any pot time. The mathematical representation of this accountg system is called a materials balance or mass balance. 2

3 onservation of Energy 3/29/2011 The law of conservation of energy states that energy cannot be created or destroyed. Meang that we should be able to account for the energy at any pot time. The mathematical representation of this accountg system we use to trace energy is called an energy balance. The simplest form of a materials balance or mass balance Accumulation = put put put Accumulation Environmental System (Natural or Device) put 3

4 ontrol Volume onsumer goods Accumulation Food to people Solid Waster 4

5 Mass rate of accumulation = Mass rate of put Mass rate of put Selam is fillg her bathtub but she forgot to put the plug. if the volume of water for a bath is m 3 and the tap is flowg at 1.32 L/m and the dra is runng at 0.32 L/m, how long will it take to fill the tub to bath level? Assumg Selam shuts off the water when the tub is full and does not flood the house, how much water will be wasted? Assume the density of water is 1,000 kg/m 3 5

6 Q = 1.32 L/m V accumulation Q = 0.32 L/m We must convert volumes to masses. Mass = (volume)(density) Volume = (flow rate)(time) = (Q)(t) From mass balance we have Accumulation = mass mass (Vacc)() = (Q)()(t) - (Q)()(t) Vacc = (Q)(t) (Q)(t) Vacc = 1.32t 0.32t 350L = (1.00 L/m)(t) t= 350 m The amount of wasted water is Waste water = (0.32)(350) = 112 L 6

7 Mass flow rate = Mass balance Efficiency of a system Mass time dm (concentration)(flow rate) c Q dm Q c Q Q Q Q OR mass mass mass The air pollution control equipment on a municipal waste cerator cludes a fabric filter particle collector (known as a baghouse). The baghouse contas 424 cloth bags arranged parallel, that is 1/424 of the flow goes through each bag. The gas flow rate to and of the baghouse is 47 m 3 /s, and the concentration of particles enterg the baghouse is 15 g/m 3. In normal operation the baghouse particulate discharge meets the regulatory limit of 24 mg/m 3. alculate the fraction of particulate matter removed and the efficiency of particulate removal when all 424 bags are place and the emissions comply with the regulatory requirements. Estimate the mass emission rate when one of the bags is missg and recalculate the efficiency of the baghouse. Assume the efficiency for each dividual bag is the same as the overall efficiency for the baghouse. 7

8 = 24 mg/m 3 Q = 47 m 3 /s = 15 g/m 3 Q = 47 m 3 /s Baghouse Accumulation = particle removal Hopper ketic reactions : reactions that are time dependent. Reaction ketics: the study of the effects of temperature, pressure, and concentration on the rate of a chemical reaction. 8

9 The rate of reaction, r i, the rate of formation or disappearance of a substance. Homogenous reactions. sgle phase reactions Heterogeneous reactions : multiphase reactions (between phases surface) r i = kf 1 (T,P);f 2 ([A],[B], ) Rate constant oncentration of reactant Assumg that the pressure and temperature are constant aa + bb c Rate of reaction r A = - k[a] α [b] β = k[] γ 9

10 Rate of reaction r A = - k[a] α [b] β = k[] γ order of reaction = α + β, the order with respect to reactant A is α, to B is β, and to product is γ. r A = -k zero-order reaction r A = -k[a] first-order reaction r A = -k[a 2 ] second-order reaction r A = -k[a][b] second-order reaction 10

11 batch reactors and flow reactors. fill-and-draw Unsteady state material flows to, through, and of the reactor IDEAL REATORS REAL REATOR 11

12 onserved system: where no chemical or biological reaction takes place and no radioactive decay occurs for the substance the mass balance. Steady-state: Input rate = Output rate Accumulation =0 Stream Wastes Q s s Q w w Decay rate = 0 Accumulation rate = 0 Q m m Mixture Q = flow rate = concentration s Q s + Q w w = Q m m 12

13 For non-conservative substances Accumulation rate = put rate put rare ± transformation rate 13

14 With first-order reactions Total mass of substance = concentration x volume when V is a constant, the mass rate of decay of the substance is first-order reactions can be described by r = -k=d/, 14

15 Decay Sewage Lagoon ontrol volume Accumulation=put rate put rate decay rate Assumg steady-state condition, accumulation = 0 put rate = put rate + decay rate Q = eff Q eff + (K)( lagoon )(V) dm/ =? d( ) d( ) 0 dm kv dm d V d k e o kt 15

16 Mass balance for each plug element dm d( ) d( ) d( ) V No mass exchange occurs across the plug boundaries, d() and d() = 0 dm d V d k e kt e k Residence time L=length The residence time for each plug: ln ( L)( A) ( u)( A) V Q ( L) k k ( u) k V Q 16

17 Time (d) Waste oncentration (mg/l)

18 oncentration, 3/29/2011 Usg the 1 st and 16 th day, the time terval t= 16-1 = 15 d t o e kt 132mg / L k (15d ) 280mg / L Solvg for k, we have k = d -1 To achieve 99 % reduction the concentration at Time t must be of the origal concentration t o 0.01 e 0.05( t) t = 92 days e 0 Time Step crease 0 Time Step decrease 0 Time pulse/spike crease 18

19 oncentration, 3/29/ Time t o e kt 1/k Time Decay 1/k Time Formation 1 1 oncentration, 0 oncentration, Time Influent concentration 0 t= Time Effluent concentration oncentration, 0 oncentration,

20 For balanced flow (Q = Q ) and no reaction, the mass balance becomes dm cq cq Where M = V. The solution is t 0 Where = V/Q t t exp 1 1 exp Flushg of nonreactive contamant from a MFR by a contamant-free fluid Which means = 0 and the mass balance becomes dm c Q Where M = V. The itial concentration is 0 =M/V For time t 0 we obta t 0 t exp 20

21 For balanced flow (Q = Q ) and first-order reaction the mass balance becomes dm Q Q k V Where M = V. By dividg with Q and V we have d 1 k 21

22 For stead-state conditions d/=0 o o 1 k OR 1 k Decay Formation o o oncentration, 0 Time 0 Time A step decrease fluent concentration ( =O) for non-steady-state conditions with first-order decay dm 0 Q k V Where M = V. By dividg with Q and V we have d 1 k o o exp t 1 k 22

23 oncentration, oncentration, 3/29/ Time Influent concentration 0 Time Effluent concentration A chemical degrades a flow-balanced, steadystate MFR accordg to first-order reaction ketics. The upstream concentration of the chemical is 10 mg/l and the downstream concentration is 2 mg/l. Water is beg treated at a rate of 29 m 3 /m. The volume of the tank is 590 m 3. What is the rate of decay? What is the rate constant? 23

24 For a first-order reaction, the rate of decay, r =-k, thus we have to solve for k from dm Q Q k For steady-state, dm/ = 0 and for balanced flow, Q = Q r k r=k=0.4 Q V Q V (10mg / L 2mg / L)(29m 3 580m 3 / m) For a first-order reaction a MFR o 1 k The mean hydraulic detention time is V Q 3 580m 20m 3 29m / m Solvg for the rate constant we get k ( o / ) 1 (10mg / L / 2mg / L) m 0.20 m 24

25 Topics Ground water pollution and remediation Global warmg and greenhouse gas effect Recent climate change and its impact Noise Pollution and ontrol Hazardous and Radioactive wastes Automobiles and the environment Product life cycle assessment A case study of a green buildg Presentation Date April 11 April 18 Topics Recyclg, reuse and resource recovery Investigate a renewable source of energy Environmental Impact of Mg Effect of limate change on Water Resource and its mitigate measures Water Quality and Treatment technologies Wastewater treatment and reuse Nanotechnology and the environment How to save our Environment Presentation Date April 25 May 2 25

26 Topics Industrial Ecology and sustaable Development Urbanization and its Environmental Impacts Environmental Effects of Natural Hazards Presentation Date May 9 visit aaucivil.wordpress.com/enveng 26

27 R epo rt fo r m at 2 0 t o 3 0 pa g e s o v e r pa g e : T i t l e a n d G r o u p m e m b e r n a m e s Ta b l e o f c o n t e n t R e f e r e n c e s L a s t D at e o f S u b m i s s i o n : J u n e 1 7, Ground water pollution and remediation Hazardous and Radioactive wastes Noise Pollution and ontrol Explore some approaches to reduce the environmental impacts of construction What can be done to make buildgs more energy efficient? Product life cycle assessment (choose specific product, e.g., cars, computers, etc) Global warmg and greenhouse gas effect A case study of a green buildg: what is green and what are the terestg design approaches (consider materials, energy efficiency, lightg, water use, etc.)? 27

28 Recent climate change and its impact Risk assessment and decision analysis Recyclg, reuse and resource recovery Investigate a renewable source of energy (such as wd, solar, geothermal), or a new technology that will reduce greenhouse gas emissions due to energy consumption (such as fuel cells or hydrogen fuel). Indoor air quality and models Automobiles and the environment Ecological Foot prts Air quality measurement and analysis 28