A method for analyzing energy used for producing a unit of mass or volume of compressed gas (specific energy consumption)

Abstract

The present invention relates to a method for analyzing energy used for producing a unit of mass or volume of compressed gas (Specific Energy Consumption) in relation to a common output flow in a compressor system, said method comprising the following pot steps:—for time interval, T.sub.ref, collecting reference measured data points of common output flow F.sub.ref and energy (or power) consumption E.sub.ref (or P.sub.ref) in the compressor system;—calculating energy (or power) use as a function of the common output flow E.sub.ref (F) (or <P.sub.ref>.sub.t(F)) from the measured data points and calculating volume output as a function of the common output flow V.sub.ref(F);—calculating average energy consumed for producing a unit of mass or volume of compressed gas as a function of the common output

flow<SEC.sub.ref>.sub.t(F) from equation E.sub.ref(F)/V.sub.ref(F) (Or <P.sub.ref.sub.t)/P.sub.ref);—for time interval, T.sub.sav, collecting measured data points of common output flow F.sub.sav and energy (or power) consumption E.sub.sav (P.sub.sav) in the compressor system;—calculating energy consumed for producing a unit of mass or volume of compressed gas as a function of the common output flow <SEC.sub.sav>.sub.t(F) from equation E.sub.sav(F)/V.sub.sav (F) (or <P.sub.sav>.sub.t(F)/F say) or SEC.sub.sav(t,F) from P.sub.sav/F.sub.sav;—calculating the difference between <SEC.sub.ref>.sub.t(F) and <SEC.sub.sav>.sub.t(F) or SEC.sub.sav(t,F) over a range of common output flow F in the compressor system.

Claims

1. A method for analyzing energy used for producing a unit of mass or volume of compressed gas (Specific Energy Consumption) in relation to a common output flow in a compressor system, said method comprising the following steps: for time interval, T.sub.ref, collecting reference measured data points of common output flow F.sub.ref and energy (or power) consumption E.sub.ref (or P.sub.ref) in the compressor system; calculating energy (or power) use as a function of the common output flow E.sub.ref(F) (or <P.sub.ref>.sub.t(F)) from the measured data points and calculating volume output as a function of the common output flow V.sub.ref(F); calculating average energy consumed for producing a unit of mass or volume of compressed gas as a function of the common output flow <SEC.sub.ref>.sub.t(F) from equation E.sub.ref(F)/V.sub.ref(F) (or <P.sub.ref >.sub.t(F)/F.sub.ref); for time interval, T.sub.sav, collecting measured data points of common output flow F.sub.sav and energy (or power) consumption E.sub.s (P.sub.s) in the compressor system; calculating energy consumed for producing a unit of mass or volume of compressed gas as a function of the common output flow <SEC.sub.sav>.sub.t(F) from equation E.sub.sav(F)/V.sub.sav(F) (or <P.sub.sav>.sub.t(F)/F.sub.sav) or SEC.sub.sav(t,F) from P.sub.sav/F.sub.sav, calculating the difference between <SEC.sub.ref>.sub.t(F) and <SEC.sub.s>.sub.t(F) or SEC.sub.sav(t,F) over a range of common output flow F in the compressor system.

2. The method according to claim 1, wherein the method involves using E.sub.ref(F), V.sub.ref(F), P.sub.sav, F.sub.sav and E.sub.ref(F)/V.sub.ref(F) and P.sub.sav/F.sub.sav in the calculations.

3. The method according to claim 1, wherein the method involves collecting data during T.sub.ref, then performing changes to the compressed system, then collecting data during the time interval T.sub.sav, and finally comparing the data.

4. The method according to claim 1, wherein <SEC.sub.ref>.sub.t(F) and V.sub.ref(F) are partly or fully simulated, constructed or are from a different compressed system than <SEC.sub.sav>.sub.t(F) (or SEC.sub.sav(t,F)) and V.sub.sav(F) (or V.sub.sav(t,F)).

5. The method according to claim 1, wherein the steps of calculating are performed over the full range of common output flow F.sub.sav in the measured data points during T.sub.sav.

6. The method according to claim 1, wherein the measurement during T.sub.sav is performed in a single data point.

7. The method according to claim 1, wherein the method involves using only a subset of the data during T.sub.ref or T.sub.sav.

8. The method according to claim 1, wherein the method involves detecting data points involving data errors and marking or removing these error data points.

9. The method according to claim 1, wherein the energy saving at flow F is calculated as
E.sub.SAVE(F)=(<SEC.sub.ref>.sub.t(F)−<SEC.sub.sav>.sub.t(F))*V.sub.sav(F)
or
E.sub.SAVE(F)=(<SEC.sub.ref>.sub.t(F)−SEC.sub.sav(t, F))*V.sub.sav(t, F) where F refers to any common output flow over the full range of measured data points.

10. The method according to claim 9, wherein the total energy saving is calculated as Σ.sub.F E.sub.SAVE(F).

11. The method according to claim 10, wherein the total cost saving is calculated as Σ.sub.F E.sub.SAVE(F)*Cost, where Cost is the cost in any monetary instrument per unit of energy.

12. The method according to claim 1, wherein SEC.sub.sav(t,F) and F.sub.sav are simulated data to analyze savings for a simulated period in time T.sub.sav.

13. The method according to claim 1, wherein any or several of the functions of E.sub.ref(F), <P.sub.ref>.sub.t(F), V.sub.ref(F), <SEC.sub.ref>.sub.t(F) and energy saving E.sub.SAVE(F) are plotted as a function against F.

14. The method according to claim 1, wherein <SEC.sub.ref>.sub.t(F) is calculated for a F having no measured data during T.sub.ref.

15. The method according to 14, wherein the method also comprises deciding <SEC>.sub.ref(F) for a F larger than the highest F, max(F.sub.ref), in the data points during T.sub.ref.

16. The method according to claim 14, wherein the <SEC.sub.ref>.sub.t(F) for a F larger than max(F.sub.ref) in the data points is set and calculated as: <SEC>.sub.ref(F)=<<SEC>.sub.t>.sub.v=Σ.sub.ref(F)/Σ.sub.FV.sub.ref(F).

17. The method according to claim 14, wherein the <SEC.sub.ref>.sub.t(F) for a F larger than max(F.sub.ref) in the data points is set and calculated by calculating Δ (difference) of <SEC.sub.ref>.sub.t(F) and SEC.sub.sav(t,F) in max(F.sub.ref) during T.sub.ref and using the same Δ for an F larger than max(F.sub.ref) in the data points to set and calculate the <SEC.sub.ref>.sub.t(F) for this F.

18. The method according to claim 13, wherein the <SEC.sub.ref>.sub.t(F) for a F larger or smaller than the highest or lowest F, respectively, measured during T.sub.ref is modelled as a piecewise continuous extrapolation of <SEC.sub.ref>.sub.t(F).

19. The method according to claim 18, wherein the model that is used to extrapolate <SEC.sub.ref>.sub.t(F) includes the situation that one or several compressors are operating their blow off valves.

20. The method according to claim 18, wherein the model that is used to extrapolate <SEC.sub.ref>.sub.t(F) includes the situation that one or several compressors are regulating using IGVs or VSDs.

21. The method according to claim 1, wherein the method comprises calculating and setting different <SEC.sub.ref>.sub.t(F) curves as a function of F for different values of a third parameter.

22. The method according to claim 21, wherein the third parameter is operational pressure for the compressor system.

23. The method according to claim 21, wherein the method also comprises plotting the different <SEC.sub.ref>.sub.t(F) curves to set a <SEC.sub.ref>(F, X) plane as a function of F and the third parameter, X.

24. The method according to claim 1, wherein the compressor system comprises multiple compressors.

Description

DESCRIPTION OF THE DRAWINGS

[0036] Below, descriptions of the drawings are presented. In FIG. 1 there is presented the basic equation models which form the starting point of the method according to the present invention. The time average SEC, i.e. <SEC>.sub.t for some time period, and as a function of flow F is obtained from E(F)/V(F). This may be one starting point for the method according to the present invention. Another route is via P/F, which then provides the instantaneous SEC at a certain time and flow, i.e. SEC(t,F). It should be noted that it is further possible to perform the calculation <SEC>.sub.t=<P>.sub.t(F)/F, i.e. calculate the time average power at a certain flow for some time period, then divide with that flow. This last route gives the same result as E/V, because <P>(F)*(time spent producing air at flow F)=E(F).

[0037] In FIG. 2 there is provided a graph visualization of a next step of the method according to the present invention. By use of the measured data points of E and V over the flow range, the value of <SEC.sub.ref>.sub.t(F) may be calculated from the equation E.sub.ref(F)/V.sub.ref(F), as understood from the description above in relation to FIG. 1.

[0038] In relation to the claims, description and drawings it should be noted that reference is often shortened as “ret”, sample as “say” and time as “t”. Moreover, and as is clear from above, energy is set as “E” and flow as “F”. This is further explained below in the section “nomenclature”.

[0039] In FIG. 3 there is shown the creation of an interpolated reference curve for <SEC.sub.ref>.sub.t over the flow range. This is then used in accordance with FIG. 4 to calculate the difference between <SEC.sub.ref>.sub.t and SEC.sub.s(t) (a), or <SEC.sub.sav>.sub.t (b), i.e. by use of SEC.sub.sav(t,F) or <SEC.sub.sav>.sub.t(F), over a range of common output flow F in the compressor system. As seen in FIG. 4, this may then be used to calculate the energy savings, given by the equation

E.sub.save(x)−(<SEC.sub.ref>.sub.t)−SEC.sub.sav(t,x))*V.sub.sav(t,x) or E.sub.save(F)=(<SEC.sub.ref>.sub.t(F)−<SEC.sub.sav>.sub.t(F))*V.sub.sav(F), which in turn may provide the total energy savings as the sum of incremental energy savings.

[0040] In FIGS. 5a-c there are provided different embodiments of the method according to the present invention, when setting values when F.sub.sav>max(F.sub.ref), that is above the measured maximal common output flow. A first alternative is presented in FIG. 5a. In this case <SEC.sub.ref>.sub.t(F.sub.sav) is set as <<SEC.sub.ref>.sub.t>.sub.v=Σ.sub.FE.sub.ref/Σ.sub.FV.sub.ref. The graphs beneath the equation show that the areas provide the sums needed.

[0041] According to FIG. 5b another embodiment of the method according to the present invention is shown. In this case, the Δ (difference) of

<SEC.sub.ref>.sub.t(F) and SEC.sub.sav(t,F) in max(F.sub.ref) during T.sub.ref is used to also calculate

<SEC.sub.ref>.sub.t(F) for a F larger than max(F.sub.ref). This is shown by the equation shown in FIG. 5b and also in the presented graph.

[0042] Furthermore, in FIG. 5c yet another embodiment of the present invention is shown. As stated in the equation, in this case <SEC.sub.ref>.sub.t(F.sub.sav)=f(F), where f(max(F.sub.ref))=<SEC.sub.ref>.sub.t(max(F.sub.ref)) and f(F) is piecewise continuous. According to this embodiment, the <SEC.sub.ref>.sub.t(F) for a F larger or smaller than the highest or lowest F, respectively, measured during T.sub.ref may be modelled as a continuous extrapolation of <SEC.sub.ref>.sub.t(F).

Nomenclature

[0043]

TABLE-US-00001 Expression Description E Energy in units of kWh. Accumulates with time. E(F) Energy consumed as a function of flow or as (similarly for a histogram with respect to flow depending any other quantity) on the situation. Example: Flow is constant at 100 m{circumflex over ( )}3/min. Then E(F) is zero everywhere except at F = 100 m{circumflex over ( )}3/min where all energy is collected, so E(100 m{circumflex over ( )}3/min) = Σ.sub.FE E(t, F) Energy as a function of time and flow (similarly for any other quantity) E.sub.save Saved energy. E.sub.save = E.sub.ref − E.sub.s P Power in units of kW. Is always a function of time unless averaged or summed over time. V Volume in units of m{circumflex over ( )}3. Accumulates over time. F Flow in units of m{circumflex over ( )}3/min. Is always a function of time unless averaged or summed over time. SEC Specific energy consumption in units of kWh/m{circumflex over ( )}3 T.sub.ref A time period for measurement of reference data T.sub.sav A time period for measurement of sample data to be compared with the reference data <X>.sub.t An average of X over a time duration. For instance <SEC>.sub.t(F) is SEC averaged over some time duration and as a function of F. X.sub.ref A quantity or value belonging to the reference data X.sub.sav A quantity or value belonging to the sample data to be compared with the reference data Σ.sub.FX(F) A sum of X over all values of flow (X has to be a function of F) <X.sub.ref>.sub.t A quantity time averaged over the time period T.sub.ref <<X>.sub.t>.sub.V Average X over time, then over volume.