Quantcast
Channel: EHSQL(Environment-Energy ,Health,Safety, Security and Social Ac. ,Quality-Lab) Technical services
Viewing all articles
Browse latest Browse all 8107

Monitor™ economic calculations answer common questions about the cost of fouling,

$
0
0

Economic Calculations

Monitor economic calculations answer common questions about the cost of fouling, the benefits to be gained from cleaning and help to develop an optimum cleaning strategy.

Cleaning Economics Reports

Monitor Cleaning Economics calculations determine the effects of cleaning exchangers in the Network.  These are shown in tabular form  and include:
  • the cost of removing exchangers for cleaning
  • the savings that could be made by cleaning selected exchangers
  • the optimum cleaning cycles for each exchanger and for user-defined groups of exchangers.
In addition, one of the standard spreadsheet reports is the Fouling Cost Summary which shows the additional costs that have been incurred over a range of cases for the furnace to make up the duty lost. 

Economic Data Required

The Cleaning Economic calculations require the following data:

Globally:

  • The Fuel Cost and the Furnace Efficiency are used when generating all economic reports. 
  • The Length of Plant Run is only used in the optimum cleaning cycle report. 
  • Fuel Cost expressed in $ per unit of duty.  The default value is the Solomon value for fuel oil.
  • Furnace Efficiency. The fuel cost is divided by this value to obtain the total cost of the fuel.
  • Length of Plant Run expressed as number of days between plant shutdowns.  This is used in the optimum cleaning cycle calculation.

For each exchanger:

  • Date Last Cleaned. This is used in the optimum cleaning cycle report.
  • Days to Clean. The number of days that an exchanger will be out of service when it is removed for cleaning.  This is used in the optimum cleaning cycle report.
  • Cleaning Cost. The fixed costs (man time, cleaning materials, etc.) associated with removing and cleaning an exchanger.  This does not include additional costs incurred by the reduced Network duty.  This cost is used in the optimum cleaning cycle report.
  • Clean Fouling Factor for the exchanger when returned to service after cleaning.  This is used in the Cleaning Economics calculation and the optimum cleaning cycle report.

How Cleaning Economics are Calculated

Fouling factors are first calculated for a selected Case.  These are used to calculate temperatures for all exchangers and at the furnace inlet.

Cost of removing exchangers for cleaning

The Network is solved and the furnace run-up temperature calculated with each exchanger in turn bypassed.  This determines the effect of removing the exchangers for cleaning in terms of lost enthalpy at the furnace inlet, also expressed as $/day. The program also calculates the amount by which the throughput would have to be reduced in order to maintain the furnace inlet temperature at its previous level.

Savings from cleaning

The fouling factor of each exchanger in turn is then set to its clean value and the Network is solved to obtain the increase in duty that this would produce at the furnace inlet.  This is shown as extra throughput which could be achieved and $/day.

Optimum cleaning cycles

The above results are then used, along with fixed costs, to calculate the optimum cleaning cycles for each exchanger.  The optimum cycle is that which minimises the annualised cost of fouling. By default, each exchanger is cleaned in turn.  Combinations of exchangers to be cleaned in addition to individual exchangers are defined in the User Defined Cleaning Economics Combinations Window.

Flexible Output

MONITOR's output capabilities are extensive.  
  • You can export the PFD drawing to PowerPoint so that you can use it in a presentation. 
  • You can get results tables displayed directly on the screen.
  • You can have a summary of Reconciliation, Fouling and NFIT runs for a range of cases.
  • You can plot results from a range of cases to view trends.

You can get the results of the current case displayed as a table directly on the screen.  
You can export these results to Word or to a Text file. 



Input Data Reprint

To enable you to check all your data, Monitor prints it all out at the start of the main results output.
The network data include:
  • connectivity 
  • mechanical data 
Case data include:
  • stream temperatures, pressures, flowrates and properties
  • exchanger temperatures
  • mixer temperatures
  • splitter ratios


Reconciliation

Monitor uses measured plant temperatures and flowrates to calculate heat exchanger fouling factors. The Data Reconciliation calculation identifies inconsistencies in the input data and enables you to obtain a more consistent set of data for the fouling calculation.
Reconciliation output shows the duties calculated from the supplied flowrates and temperatures for each side of target exchanger and the differences between them. It also shows the differences between the target and calculated temperatures of the  products of target mixers.
The same data are then shown after the reconciliation has been completed. The table shows by how much feed stream temperatures and flowrates and splitter ratios have been changed to achieve a reconciled data set.


Fouling

After a reprint of the input data, the fouling report shows tabular results for each type of heat exchanger in turn, followed by results for all other types of unit operation in turn. Finally, the temperatures, pressures, flows and properties are presented for all the streams in the Network. 
Heat exchanger results include:
  • Exchanger duties, clean and dirty coefficients
  • Tube and shell velocities and Reynold's Numbers
  • Mixer temperatures and duties
  • Stream temperatures, rates and properties.


Normalised Output

Normalisation is the technique Monitor uses to remove the effect of the changes in external parameters, such as crude and product variations, to determine a true picture of the degradation of network performance due to fouling alone.
The calculated fouling factors from each case are superimposed onto the feeds from a selected base case and the resultant temperatures reported.
Normalisation output includes:
  • fouling resistances used
  • exchanger exit temperatures
  • run-up stream temperature



Cleaning Economics

Cleaning Economics calculations determine the effect of cleaning exchangers in the Network and an optimum cleaning cycle for each exchanger.
Cleaning output includes:
  • The cost of removing each  exchanger as the additional fuel cost/day to make up the duty and as the loss in throughput if the duty was not made up by the furnace.
  • The increase in duty of the complete Network after each exchanger has been cleaned expressed as a reduced furnace cost to maintain current operation and an increased throughput which could be achieved if furnace duty was not reduced.
  • The Optimum Cleaning Cycle period which provides the lowest annualised cost of fouling. The savings shown are compared with the cost of cleaning once at the end of the plant run.



Splitter Optimisation

Splitter Optimisation determines splitter product ratios which maximise the heat recovery of the Network. This minimises the required furnace duty for the Network.
Optimisation output includes:
  • Initial and final enthalpy and temperature of the chosen run-up stream.
  • all exchanger inlet and outlet temperatures and flowrates at the optimum splitter setting.


Calculation Histories

This report summarises the Reconciliation and/or Fouling and/or NFIT results for all cases within a range you select.It is particularly useful for troubleshooting data errors.  
The report here shows a range of Data Reconciliation results, including some failed cases.
You can choose to display all cases or just failed cases.

 

Plotted Output


For monitoring over a time period, by far the most meaningful form of output is that presented in graphical format.
There are a number of standard, predefined reports. You may also define your own reports to include the parameters, units and/or streams that you require.
The data for the selected report are written to a text file which is then opened automatically in Excel. A plot is created for each set of data in the spreadsheet. You may then modify and save the workbook or copy plots or data into other applications.
The standard reports are:


Reconciliation

This report compares results for data reconciliation over the range of Cases. It shows:
  • the initial duty imbalance for target exchangers and the initial and final duties on the shell and tube sides for each exchanger.
  • changes in flowrate and temperature of feed streams.
       

Heat Transfer

This report contains heat transfer data for all the exchangers in the Network and any normalised furnace inlet temperatures.
For each exchanger there are plots for:
  • duty
  • fouling
  • U-values .. clean, actual and normalised
  • tube velocity
  • shell velocity
  • effectiveness


Fouling Cost

This report shows the additional costs incurred when a furnace makes up the duty lost because of fouling. 
The spreadsheet plots the following on separate worksheets:
  • The normalised furnace inlet temperature.
  • The Cost/day of the additional furnace duty required to make up for the network duty loss caused by the current level of fouling.
  • The cumulative additional furnace duty required since the start of the specified period. 
  • The cumulative fuel cost of the exchanger fouling since the start of the specified period.


Stream Temperatures

This report shows the temperatures of all streams in the Network. 
Feed streams, product streams and internal streams are presented separately and are plotted on separate worksheets.
Compare this plot of the actual furnace inlet stream temperatures with the normalised plot abov.  This shows the benefit of normalisation to give a more meaningful presentation of the true effect of fouling. 


Weight and Volume Flow Rates

These two reports show the weight and volume flowrates of all streams in the Network. Feed streams, product streams and internal streams are presented separately and are plotted on separate worksheets.

Weight Flowrates
Volume Flowrates

Pressures

The pressure at the inlet and outlet of each exchanger is listed on this report along with pressure drops. The plots for each exchanger are on separate worksheets and show:
  • Shell side inlet and outlet pressures
  • Shell side pressure drops
  • Tube side inlet and outlet pressures
  • Tube side pressure drops


User Defined Spreadsheet Outputs

If none of the standard spreadsheet reports meets your requirements, you may define your own reports.
You may specify a
  • Exchanger duty, U (actual and clean), fouling factor, velocities, Re, temperatures, MTD, LMTD and Ft.
  • Pump duty, heater and cooler temperatures and splitter ratios.
  • Stream temperatures, pressures, flowrate and liquid fraction. 



Viewing all articles
Browse latest Browse all 8107

Trending Articles