billbill20002000
Chemical
Hello Group,
I am trying to set up a spread sheet to help us schedule cleaning of our HX's. I found an article on the CEP magazine in which a technique using EUAW (equal Uniform Annual Worth) is used. After Google for 2 days I haven't been able to find how to do this. The article describes using a first order model to predict the change in the U of the exchanger byt the following equation:
U=Uo*e^-kt
Where k is the rate of fouling calculated from operation data
t is the time (yr o month)
Uo=U when the exchanger is clean
Now once I have this data I will create table in which the actual value of U from year 0 (when clean) to year 1,2, etc. I will tabulate the value of U, the diference between Uo and U for each year. Now Here is the part where the article stops at describing the calulation. In the table you have an incremental hot and cold utility cost.
The data for the example is:
MAR (minimum aceptable Return)=20 DCF (any idea what this means?)
Tax rate 34%
Hot utility cost $5/MMBtu
cold Utility $0.5/MMBtu
Operation time 8760 stream hr/yr (100% factor)
now in the table you get:
year Process duty Trim Duty Incremntal Incremental
MMBtu/h MMBtu/h hot Utility Cold Utility
$/yr $yr
0 10 0 0 0
1 9.93 0.07 3269 327
2 9.76 0.24 10415 1042
etc
1. I am stuck on how they are calculating the incremental utility cost
2. Once they have this, the obtained plots of EUAW vs time for different values of k and total cleaning costs, How do you think they went from what you have in the table to EUAW's? all they say is that:
"Using the decline of U over time, one can calculate the duty of the process exchanger from the end of year 0 to the end of years 1, 2, 3, and so on, by solving Eqs. 1–3 (which Are:
Q=Mh*Cph*(T1-T2)
Q=Mc*Cpc*(t1-t2)
Q=A*U*LMTD)
simultaneously. Because energy not recovered in the process exchanger must be made up in the trim exchangers, ncremental increases in utility costs that result for each year of the analysis can also be calculated. Cleaning is a one- time expense, which is assumed to return U to its original (i.e., clean exchanger) value. Figure 2 plots U vs. time for various cleaning schedules.Cleaning changes the project life, or analysis period, to the number of years between cleanings. A cash flow analysis is used
to find incremental increases in operating expenses until the year of cleaning. Cleaning is treated as a year zero cost for a new analysis period. Discounted cash flow is used to calculate a net present value for the cleaning and subsequent incremental operating costs. From the net present value, an EUAW can be calculated based upon the life of the project between cleanings. Using EUAW allows a direct comparison of results between projects with varying life spans. Plotting EUAW vs. cleaning schedule reveals the maximum annual worth or optimum cleaning schedule. "
I havent been able to figure out or reach the author of this, there is a second example without a tax rate and still they get a plot of EUAW but no description on the method. Any comments, references, experiences on scheduling or articles will be appreciated it.
Cheers
William
I am trying to set up a spread sheet to help us schedule cleaning of our HX's. I found an article on the CEP magazine in which a technique using EUAW (equal Uniform Annual Worth) is used. After Google for 2 days I haven't been able to find how to do this. The article describes using a first order model to predict the change in the U of the exchanger byt the following equation:
U=Uo*e^-kt
Where k is the rate of fouling calculated from operation data
t is the time (yr o month)
Uo=U when the exchanger is clean
Now once I have this data I will create table in which the actual value of U from year 0 (when clean) to year 1,2, etc. I will tabulate the value of U, the diference between Uo and U for each year. Now Here is the part where the article stops at describing the calulation. In the table you have an incremental hot and cold utility cost.
The data for the example is:
MAR (minimum aceptable Return)=20 DCF (any idea what this means?)
Tax rate 34%
Hot utility cost $5/MMBtu
cold Utility $0.5/MMBtu
Operation time 8760 stream hr/yr (100% factor)
now in the table you get:
year Process duty Trim Duty Incremntal Incremental
MMBtu/h MMBtu/h hot Utility Cold Utility
$/yr $yr
0 10 0 0 0
1 9.93 0.07 3269 327
2 9.76 0.24 10415 1042
etc
1. I am stuck on how they are calculating the incremental utility cost
2. Once they have this, the obtained plots of EUAW vs time for different values of k and total cleaning costs, How do you think they went from what you have in the table to EUAW's? all they say is that:
"Using the decline of U over time, one can calculate the duty of the process exchanger from the end of year 0 to the end of years 1, 2, 3, and so on, by solving Eqs. 1–3 (which Are:
Q=Mh*Cph*(T1-T2)
Q=Mc*Cpc*(t1-t2)
Q=A*U*LMTD)
simultaneously. Because energy not recovered in the process exchanger must be made up in the trim exchangers, ncremental increases in utility costs that result for each year of the analysis can also be calculated. Cleaning is a one- time expense, which is assumed to return U to its original (i.e., clean exchanger) value. Figure 2 plots U vs. time for various cleaning schedules.Cleaning changes the project life, or analysis period, to the number of years between cleanings. A cash flow analysis is used
to find incremental increases in operating expenses until the year of cleaning. Cleaning is treated as a year zero cost for a new analysis period. Discounted cash flow is used to calculate a net present value for the cleaning and subsequent incremental operating costs. From the net present value, an EUAW can be calculated based upon the life of the project between cleanings. Using EUAW allows a direct comparison of results between projects with varying life spans. Plotting EUAW vs. cleaning schedule reveals the maximum annual worth or optimum cleaning schedule. "
I havent been able to figure out or reach the author of this, there is a second example without a tax rate and still they get a plot of EUAW but no description on the method. Any comments, references, experiences on scheduling or articles will be appreciated it.
Cheers
William
