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Energy recovery and monitoring for a calm future
Article taken from"Automazione e Strumentazione" - issue 8 - September 1997

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An interesting experiment carried out in the province of Bergamo proved that initiative along with technology and innovation, is the best way to increase life quality, even in an uncertain Italian political phase for the energy scenario.

By Aldo Fiocchi

BAS S.p.A. (Bergamo Ambiente e Servizi) is a company merged from two municipal concerns managing respectively water, natural gas and public lighting the one, and the urban rubbish collection, its relative thermodestruction and water purification the other.
This company constitutes one of the few (but in fact destined to increase) examples of "functional" privatization with satisfactory results since 1994. The city of Bergamo picks up natural gas at a pressure of 64 bar (according to what detectable by the methane pipeline, given that the effective pressure varies in operation with the seasons and the functioning of the methane pipeline itself) from three Snam supply points located respectively in Zanica (the main one) with a 23,500 m3/h standard capacity, in Grumello with 10,000 - 12,000 and in Tremana with 4,500. Later on, right after an intermediate decompression at 2,5 bar through lamination of reducing valves, the gas feeds district and user booths for final decompression: after an accurate analysis it however revealed that the lamination phase involved the dissipation of pressure energy (the so-called "noise"), so the opportunity of converting this "noise" into "active" electric energy with an original solution to act as reference also for others, obviously with the involvement of CEE, was considered from both technical and economical point of views.
Because of this, a first project arose in the 1992, which was not well appreciated as it was not considered innovative enough: BAS turned then to the Politecnico di Milano, which thanks above all to the contribution of Engineer Carlo Piemonte, solved the problem with a new project called EASE (Efficient All Seasons Expander), based on the integration of a plant for recovering electric energy from gas with a cogeneration system.
The gas arriving to the decompression booth of Via Zanica in Bergamo was handled by two alternative piston expanders joined to an unique electric generator with two shaft heads. One of the expanders was designed for low capacities (summer season) allowing the recovery of 500 kW of electric power, while the other developed for middle-high capacities (end of autumn season - beginning of spring) allowed the recovery of around 850 kW.In the winter season (December-February), because of the large quantitative of gas required, both expanders were working simultaneously.Thanks to the cogeneration group, composed of two Otto engines of 826+657 kW of electric capacity, the recovered thermal energy was used for the heating of natural gas to send to one or both expanders.
It is useless to say that at this point, the CEE approved it and, after a year of work EASE was a reality.

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The expanders and the generator were supplied by Spillingwerk Gmbh of Amburgo, while the Techint company of Milano provided for the structures and final assembly.
The plant had almost completed the starting phase and was working automatically, even if for precaution, the presence of a control operator for emergency interventions was settled.
With this situation, on September the 21st, 1996 the plant was officially presented to the authorized personnel in a convention about "Safety in the use of gas and energy optimization" which was held at the Centro Congressi "Giovanni XXIII" of Bergamo.
At this point, it became important to make all information regarding the functioning of the plant available, so as to constitute a "permanent dossier" as reference for technical data, for the IEN (Indice Energetico) and other types of documentation to be sent, as always, to the CEE for successive revisions.
At first, the acquisition procedure of this information was manual only, also because the first objective was about reaching the optimal functioning level of the plant in a short time. That was why each further automation was postponed: once verified that the effectiveness index of the plant was superior to 0.5 and, therefore, compatible with the project specifications and also with everything at the basis of the convention drawed up with the CEE, the phase concerning the supervision took the go, but...how could this problem be practically solved? "Of course not dealing with it by ourselves" says Giulio Borselli (responsable of the Monitoring and Automation sector of BAS S.p.A.), "as it is not included in our qualifications: we are proud, or maybe presumptuous, to know how to distribute water and gas, therefore any other subject that is not part of this concern others".
And here came Automa, the well-known company of Pedrengo specialized in high-level applications, which undertook the charge of creating an adequate supervision and control system. The company satisfied completely the expectations with the development of a dedicated software, which in short, is a Super-Flash application, the well-known supervision system. In this particular circumstance, the connection between the local station and the remote workstations was developed as to, while the Personal Computer located close to the plants carries out its own activities, the remote PC located inside the monitoring office where information relative to water and gas plants is also collected, be connected to a non-switching telephone line in order to avoid network interferences and therefore possible communication errors. The connection was developed considering that the authorized personnel is present eight hours a day for five days a week, while the data and information collection concerns the space of 365 days, that is a year, 24 hours a day.

On the control bridge
The plant is controlled with a local PC connected through a RS 232 serial line functioning 24 hours a day with the purpose of managing states, alarms and measurements to then acquire data at a specific time for producing daily and monthly operation reports. A modem accessing two remote PC with different functionalities, first-level functionalities (with all options enabled) and second-level ones (with only some options enabled) respectively, and a printer are connected to the local PC.
The softwares of the two remote PC and the local one have the same graphic interface; what makes them different is, in fact, their possibility to be connected through a modem.

Leafing through the pages
The supervision of the plant is carried out by a computer through "pages": the main page shows a graphic of the two expanders with indicators for states or alarms coming from "critical" points of the plant in order to report eventual malfunctionings.
The system acquires 31 measures of various types, as well as, states and alarms refered to the Snam supply point, the two expanders and the measurement points. In particular, some colors are used to identify the valves status: green or red for the "open" or "closed" status, while grey identifies the unknown status of valves performing a not critical function for the good functioning of the plant.
The next step involves the part relative to the thermal power station where the main objective is the management of states (two pumps and a boiler) and alarms (temperature and pressure). The 31 measures relative to the two pages above mentioned are acquired and sampled to produce the daily reports that may be also consulted graphically (trend). On this subject, a grouping of significant data (input values, values relative to expanders and output values) was suggested so that they could be easily managed by the authorized operators.
Each graphic is highlighted with an appropriate color, having also the possibility to perform zoom and scroll operations.
The data sampling is realized in order to obtain a new data acquisition every ten seconds, after this the average of the acquired data is calculated every five minutes (in fact, in this short time interval the variations of temperature may be meaningful). Later on, an hourly average is calculated over those results to then determine a daily average. Exactly for this reason, it is possible to decide in the page relative to the thermal power station how to measure the graphic (hourly, daily, weekly, monthly): in this way the sampled curves can be visualized in various "time intervals". As an example, on an hourly basis it is possible to visualize the curves resulting directly from the high frequency sampling data coming from the plant and, which therefore, represent a significant analysis of the data itself, while from the point of view of data consulting, the daily basis (sampled data every five minutes), the weekly basis (sampled data every hour) and the monthly basis (sampled data everyday) become important in order to manage correctly the functioning and efficiency of the plant.
The system also includes a page dedicated to the synoptic of the plant, where all the indicators may be lighted up in red to report an alarm or in yellow to identify a state: both events are correlated as an inopportune "state" variation will generate an "alarm", as for example in the case of an open or closed gate valve with an anomalous change of vapour temperature verified.
Around the same principle above mentioned, another page displaying a table with the 31 measures acquired, along with the description, acronym and current value of each single measure was created.

Management and timing
Moreover, special modules had been developed on the remote PC only, as for example the one relative to report generation, consulting and management, for visualizing reports previously created, printing them, copying them and even deleting them.
A daily report contains the hourly values of the 31 measures: the data is produced in an ASCII file in order to be able to be imported/exported to an EXCEL file and, what is even more important, the data can not be modified in the measurement phase being it possible in the processing one.
The monthly report is analogous to the daily one with the difference that the samples and the measures are refered to days instead of hours: in this case the "critical" measures to keep under control are only seven and, what's more all the relative data have an annual "historical report". Through the remote PC, it is possible to control the "current" situation of the plant and the "download" of the data relative to the 31 sampled measures with the methods previously explained, the states and the alarms (along with their historical reports). This last operation can be carried out automatically or manually: if automatically, the date of the last download is at first saved keeping the continuity in the next data downloading operations and, therefore updating continuously the situation, while if carried out manually, this operation concerns, as for example, the situation relative to a particular day.
By enabling the downloading command, the date of the operation appears on the video, as well as, the progressing status while a logger provides starting date and time of the downloading phase "every minute", indicating possible irregularities.
In order to allow the connection of a remote PC to the plant, some appropriate configuration parameters must be set. After this, it is necessary to activate the right command for the connection: an appropriate page indicates if the connection with the local PC was successfully activated.
Also in this case, a logger explains the same functions above mentioned for the data downloading (starting date and time of the various connection requests, possible problems coming during the connection and ending date and time of the connection), functions that however are aimed to calculate the using time of the telephone line.

Statistics and remote...control
One of the two remote PC is a permanent one, while the other is a portable one. This is because only the monitoring operator on duty is physically present in the production phase of electric energy in the time band over the 5:00pm. The technical responsible on duty in that period must be able to get connected directly from his home through a portable PC to keep the complete situation under control, as well as, take the relative decisions in case of possible proThe supervision system also has other service options such as an address book with the possibility to be updated from time to time, the printing of the graphic pages examined, a page with the report of all alarms and states with the date and time they occurred.From this page it is also possible to access the "historical report" of those events, thanks to the daily management of an appropriate file at an annual basis, and therefore review the functioning of the plant from the point of view of the alarms or states, or on the other hand process the statistics about a single alarm or state (the number of occurrences of each alarm, the minimum, average and maximum duration, the last time it was verified and how long it lasted).blems.
At this point it is possible to determine for a specific alarm or state, in a given period, how many times that event occurred, its total duration, information about the last occurence and if the alarm or state is still in progress, when it started and from how long it is lasting. Moreover, it is possible to extract data relative to the totality of alarms and states by duration and number of occurrences.
In order to make the alarm disappear from the screen (In order to lose the alarm signal from the display), it must be accepted: this type of action is however possible from the local position only. Besides, there is an indicator relative to debugging operations for the errors found on the peripherals.
To conclude, the system does not have commands available as it is about pure monitoring and, on this subject, it is interesting to notice that some measures are double sampled according to the redundancy concept, exactly for the importance of what they represent.
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