1	CSChE 2002, Thermal Pinch Analysis Energy Reduction Cost-effectiveness of Process Simulation and Pinch analysis Chris Connaghan, P.Eng., Duncan Industrial Gaétan Noël, M.Sc. Eng., Pragmathic Larry Wasik, P. Eng., Aurel Systems
2	Why should I use Process Simulation and Pinch analysis ? Often heard reasons for lack of interest: Too expensive: it generates no savings by itself and has no payback ! We do not need that, we already know what to do ... Energy efficiency is often not profitable, paybacks are always much longer than the studies indicate ! Our processes change continuously, any study results will only be valid over a few months period As a consequence, payback of installed projects takes longer
3	The Context Mills are complex with many interrelated systems Energy savings in one department may simply cause additional energy usage in another department Improving energy efficiency in a major way needs a dedicated approach This approach is Computer Simulation and Pinch analysis Many case studies can now show the benefits of this expertise
4	Process Simulation of an Entire Pulp and Paper Mill It is now possible to simulate a complex integrated mill with a single computer simulation The energy saving of a given project can be determined rigorously all interactions between the different components of the process are taken into account by the simulation high level of confidence for the predicted energy savings
5	Cadsim+ Simulation of a TMP Mill Entire Mill Requires 4 AO Drawings
6	Process Simulation and Pinch Analysis deliver fast Paybacks Precise information provided by the process simulation It gives information on the energy efficiencies of your processes, equipments and unit operations It allows the identification of problems that can often be easily and cheaply solved The approach and thinking process governing the streams selection for the Pinch analysis study generates many profitable findings Some examples to come
7	Process Simulation and Pinch Analysis deliver fast Paybacks In consequence, the study itself has its own payback Short payback of a few months Based on the authors’ experience, there has been no exception to this rule so far for any mill
8	Example 1 - TMP mill in BC Quesnel River Pulp, 2001 The process simulation has shown: Severe fouling of the heat exchanger used for effluent cooling by energy recovery Exchanger cleaned
9	Example 2 - TMP mill in BC (Quesnel River Pulp), 2001 The process simulation has shown: Severe fouling of the TMP reboiler Reboiler retubing has been done
10	Example 3 - TMP mill in BC Quesnel River Pulp, 2001 From the Pinch Analysis streams data extraction phase: Fresh water can be displaced by ww for the chips impregnation on TMP lines 1 and 2 •savings around 200k$/yr • very cheap project • refunds the study within a few months
11	Example 4 - TMP mill in BC (Quesnel River Pulp), 2001 From the Pinch analysis streams data extraction phase: Excess pressurized contaminated TMP steam from any of the 3 lines can be sent into the chip bins of any other line when fresh steam is consumed Savings around 650 k$/yr with a very small payback Precise contaminated steam balance helps greatly to catch these opportunities
12	Example 5 - Another TMP Mill in BC, 2001 From the Pinch Analysis streams data extraction phase: Possible to recycle a reclaim screen effluent to the chip washer Confirmed with the process simulation Very cheap modification with savings around 150 k$/yr
13	Precise Methodology =Precise Payback Example 6: TMP clear ww cooling by energy recovery: air preheating of the pulp flash dryers The following project had been submitted to management Savings given were around 780 k$/yr Anticipated payback of 13 months
14	Precise Methodology = Precise Payback Process simulation shows that only 25% of estimated savings would happen Cooler ww means less steam generated by the refiners Cooler ww reduces the existing amount of energy already recovered from the TMP Now the corrected payback requires 52 months instead of 13 months !! This is an example where a waste of capital can be avoided
15	Precise Methodology = Precise Payback Question: what is the minimum ww temperature that can be set with no penalty to the energy recovery potential ? Pinch Analysis can answer such a difficult question using composite curves Capital cost can even be assessed ahead of any design!!
16	Precise Methodology = Precise Payback Pinch Analysis can then be used to correctly identify the profitable options to cool ww With the correct evaluation of the savings using the computer simulation The computer simulation output is used to modify the streams’ data set used for the Pinch analysis next slide: example
17	Precise Methodology = Precise Payback Computer Simulation is used to modify the streams’ data set for the Pinch Analysis
18	Do you really know what are your best options ? Example 7: TMP Pulp Mill in BC Steam boiler feedwater preheating often on the wish list of all mills What about if you can shut the boiler off¹ or reduce its load drastically within a 1 yr payback ? Pinch analysis and computer simulation can avoid a waste of capital expenditure Note 1 : Obviously, not all mills can afford to shut all the boilers off because of process constraints
19	Do you really know what are your best options ? Example 7: TMP Pulp Mill in BC
20	Do you really know what are your best options ? Example 8: Kraft Mill in Qc Large flowrate of cold ClO₂ solution used for the bleaching Mill’s suggestion: heat the solution with some hot condensate Composite curves show this is a non-optimal choice
21	Do you really know what are your best options ? Example 9: TMP Mill in Qc Target: cool the effluent to 37 deg. C Composite curves show this is impossible with the current operating conditions
22	Do you really know what are your best options ? Option: consider judicious process modifications To achieve that correctly, Process Simulation is mandatory Solution: increase temperature set point of the TMP ww network to 76°C
23	Wrap up... so far You may think that some of the previous examples are very simple, obvious and easy to identify projects, but remember that... A well done job using rigorous approaches often delivers crystal clear solutions that follow the KISS rule: Keep It Simple Stupid This is a usual consequence of Pinch Analysis and Computer Simulation
24	A mill is a living process that changes continuously... Major changes frequently occur and can impact the selected projects of an energy efficiency program A possible approach: include some flexibility in your plan of action A few alternate solutions from Pinch Analysis design rules can be found for a given selected value of dT_min This gives options to the mill and add some flexibility to the solutions presented
25	A mill is a living process that changes continuously... Ex. 10 (QRP): ww heating for the bleaching: 2 options
26	A mill is a living process that changes continuously... ... leading to a flexible road map of (as much as possible) independent projects
27	Conclusions Computer Simulation and Pinch Analysis have come of age Now it is possible to simulate complex integrated mills in a single simulation Energy saving projects identified the conventional way cannot bring the mill to its maximum energy efficiency potential and can lead to some waste of capital With the existing trend resulting from the Greenhouse gases concerns and the Kyoto protocol, this approach is a powerful tool available to minimize a mill’s CO₂ emissions in a profitable economic context