Patent Description:
A biogas plant is classified according to the operating purposes (environmental clean-up or energy recovery) or according to the management methods (manual control or automatic control). The main elements forming a system for automatically adjusting the gas taken up from wells are:.

The adjusting stations include the well line terminals, the condensate separators, the shutoff valves, the adjusting valves, and the gas sampling system.

The control system allows centralizing the management of the plant operating functions. The usage system allows energy recovery and electrical energy production. Adjusting the plant allows extracting a gaseous mixture while adjusting the percentage of oxygen and/or the stable and elevated methane value and/or the quantity of biogas extracted corresponding to the production curve, according to needs and/or circumstances.

As known in the background art, the uptake plants of the biogas produced by waste degradation comprise:.

The biogas production mechanisms relate to generating compounds in gaseous phase, through vaporization, biological breakdown and physical/chemical reactions.

The main factors affecting the quantity and quality of the emissions are the type of waste and the landfill conditions (in which the waste is contained) in terms of temperature and years of cultivation. The production of biogas generally is estimated by means of a known software product such as GasSim2. <NUM>, which is the most well-known in the background art. In order to estimate the intake flow rate of the biogas, the intake flow rate of each biogas well, and of the whole landfill overall, needs to be determined. For the uptake of the biogas, a system for this function comprises the following elements:.

The transport network consists of items and pipes connecting the landfill uptake points to the intake control station. The automatic adjustment of the extraction parameters aims to recover energy, where the percentage of methane is essential for the automatic adjustment, and therefore, where it becomes necessary to analyze the components of methane, oxygen and carbon dioxide contained in the gas.

A system of this type is known, for example, from <CIT>.

The uptake systems according to the background art have the problem - dealt with and overcome by the present invention - of modulating one or more valves in order to ensure the flow rate and quality required.

The solution proposed according to the present invention is based on the analysis of the oxygen content from the biogas streams extracted from landfill wells and on continuously analyzing the content of the stream formed by mixing the various streams. The opening of the valves located along the respective intake lines from the wells is modulated based on the oxygen content so that the oxygen content of the mixed stream is less than the predetermined limit value.

The control station adjusts the opening of the valve involved by the stream and positioned along the respective well intake line in order to vary and modulate the flow rate intake based on the oxygen content for the single stream. Thereby, if the oxygen value is less than the desired limit, the valve opening is increased so as to increase the gas intake flow.

According to an embodiment, the system for automatically adjusting the gas uptake from wells of the present invention comprises:.

According to an embodiment, a well control station cyclically analyzes the oxygen content of the biogas streams extracted from the landfill wells and continuously analyzes the oxygen content of the stream obtained by mixing the various streams.

According to an embodiment, the control station manages the modulation of the valves to ensure the flow rate required by monitoring the oxygen value in the biogas mixture at a predetermined value. Based on the oxygen content detected for the single stream, the adjustment system adjusts the opening of one or more valves positioned along the respective well intake lines in order to modulate the flow rate intake; thereby, if the oxygen value were less than the desired limit, the opening of one or more valves is increased so as to increase the gas intake flow from the well; vice versa, the opening of one or more of the valves is reduced if the oxygen value is greater than the predetermined limit. The valves operate according to the modulating set point based on the deviation of the value measured for the N-th well from the average of the wells.

The object of the system is to allow keeping a set point for the oxygen concentration by correcting the single intake lines of the collected wells; according to an embodiment, the system can be accompanied by a system for measuring the flow rate by means of a calibrated orifice and differential pressure transmitter. Simultaneously, according to an embodiment, the system can also analyze the oxygen content of the main stream obtained by mixing streams from various wells, and make corrections by increasing or limiting the intake of the single lines: if the oxygen content of the main stream is less than the desired limit, the opening of all the valves located along the intake lines is increased; vice versa, the opening of the valves is reduced if the oxygen value is greater than the limit.

This last control can also communicate with a blower controlled by adjusting the number of revolutions to perform a suitable control of the gas intake.

Further features and advantages of the invention will become more apparent from the non-exclusive description of the embodiments of the present invention shown in the drawings, in which:.

In the drawings, the system according to an embodiment of the invention therein depicted is identified by the reference numeral <NUM> and comprises a plurality of intake lines (pipes) <NUM>, <NUM>,. , 100n, each extending between a respective well (not shown in detail) and a manifold <NUM>, where the gas extracted (exiting) each well is introduced into manifold <NUM> by means of lines or pipes <NUM>, <NUM>,. , 100n, the gas lastly being sent from manifold <NUM> to a plant (not depicted) by means of a further pipe.

Moreover, reference numeral <NUM> identifies a sensor in connection with each of the pipes <NUM>, <NUM>,. , 100n by means of respective tapping pipes <NUM>, <NUM>,. , 120n by means of which part of the gas transiting in the pipes <NUM>, <NUM>,. , 100n is sent to sensor <NUM>, said sensor <NUM> being adapted to measure the percentage of oxygen O<NUM> transiting in each pipe <NUM>, <NUM>,.

Each pipe <NUM>, <NUM>,. , 100n is further equipped with a respective valve <NUM>, <NUM>,. , 130n, where the degree of opening of each valve <NUM>, <NUM>,. , 130n determines the quantity of gas transiting in the respective pipe <NUM>, <NUM>,. , 100n, where the opening and closing of the valves <NUM>, <NUM>,. , 130n is obtained by means of respective actuators <NUM>, <NUM>,. , 140n in turn controlled by respective logics <NUM>, <NUM>,. , 150n, each of which is electrically fed by means of a secondary electric line <NUM>, <NUM>,. , 160n, the secondary lines <NUM>, <NUM>,. , 1600n being connected by a main electric line <NUM> connected to a main logic for managing sensor <NUM>.

The gas mixture coming from the single wells along the respective pipes <NUM>, <NUM>,. , 100n; said mixture transiting in the discharge pipe (towards a plant, not depicted) <NUM> is monitored by means of an analyzer <NUM>.

The system (also possibly referred to as "control station") is conceived to ensure the percentage of oxygen O<NUM> in the gas mixture transiting in the discharge pipe <NUM> never exceeds a predefined limit value, referred to as the "DESIGN SET POINT", where the operating modes of system <NUM> can be summarized as follows.

The system is conceived to cyclically analyze (by means of sensor <NUM>) the oxygen content of the biogas streams extracted from landfill wells and therefore, transiting in the pipes <NUM>, <NUM>,. , 100n, and continuously analyze (by means of the analyzer or sensor <NUM>) the oxygen content of the stream transiting in the discharge pipe <NUM> (obtained by mixing the various streams transiting in the pipes <NUM>, <NUM>,. As mentioned, for this purpose, part of the gas transiting in the pipes <NUM>, <NUM>,. , 100n is tapped and sent to sensor <NUM>, which measures the percentage of oxygen O<NUM> thereof. Similarly, part of the mixture transiting in the discharge pipe <NUM> is tapped and sent to sensor <NUM>,which measures the percentage of oxygen O<NUM> thereof. Based on the oxygen content (percentage) of the gas mixture in pipe <NUM>, the opening of one or more of the valves <NUM>, <NUM>,. , 130n located along the respective intake lines <NUM>, <NUM>,. , 100n from the wells is modulated so that the oxygen content of the mixed stream transiting in pipe <NUM> is less than said predetermined limit value (DESIGN SET POINT).

Analyzer (sensor) <NUM> analyzes each supply pipe separately by opening the respective dedicated valve <NUM>, <NUM>,. , 130n, where based on the oxygen content read for the single stream or pipe <NUM>, <NUM>,. , 100n, the system adjusts the opening of the respective valve <NUM>, <NUM>,. , 130n, thereby varying the flow rate intake; if the oxygen value is less than the desired limit, the opening of valve <NUM>, <NUM>,. , 130n is increased so as to increase the gas intake flow from the respective well; vice versa, the opening of the valve is reduced if the oxygen value is greater than the limit.

The valves operate according to a modulating set point based on the deviation of the value measured for the N-th well from the expected set point value. (Δ AT-XX)
The steps of increasing/decreasing the opening of the single valves <NUM>, <NUM>,. , 130n are in the range <NUM>-<NUM>% according to the deviation (Δ AT-XX = 130n(XX) - DESIGN SET POINT), as described in the following example, where 130n(XX) is the percentage of oxygen read by sensor <NUM> for the single valve 130n.

If 130n(XX) ≤ than set point "%O2 design" -> the valve 130n opens according to the table.

If 130n(XX) > than set point "% O2 design" AND
value read by <NUM> < than set point "% O2 design" -> the valve 130n opens by Y5.

If the value read by <NUM> ≥ than set point "% O2 design" -> the valve 130n closes according to the percentage values in the table below.

System <NUM> is therefore capable of keeping a set point for the oxygen concentration by correcting the single intake lines <NUM>, <NUM>,. , 100n from the collected wells.

According to an embodiment, system <NUM> can be accompanied by a system (not depicted) for measuring the flow rate by means of a calibrated orifice and differential pressure transmitter.

As shown, system <NUM> also analyzes the oxygen content of the main stream (%O<NUM> manifold <NUM> towards utility) obtained by mixing streams from the various wells and makes corrections by increasing or limiting the intake from the single lines <NUM>, <NUM>,. In particular, if the oxygen content of the main stream (in manifold <NUM> and/or in the discharge pipe <NUM>) is less than the desired limit (DESIGN SET POINT), the opening of one or more of the valves <NUM>, <NUM>,. , 130n located along the intake lines <NUM>, <NUM>,. , 100n, respectively, is increased; vice versa, the opening of the valves <NUM>, <NUM>,. , 130n is reduced if the oxygen value is greater than the limit.

System <NUM> is modular and each module can collect and monitor up to <NUM> lines <NUM>, <NUM>,.

It has therefore been shown, by means of the following description of the embodiments according to the present invention depicted in the drawings, that the system according to the invention allows the desired results to be achieved and the drawbacks found in the systems according to the prior art to be overcome.

Although the system according to the present invention was clarified by means of the following description of the embodiments depicted in the drawings, the system according to the invention is not limited to the embodiments described and shown in the drawings. Contrarily, all those variants of the embodiments described and depicted in the drawings which are obvious to skilled experts in the field fall within the objects of the present invention.

Claim 1:
A system (<NUM>) for automatically adjusting the percentage of oxygen in the gas taken up from wells, said system comprising:
a plurality of pipes (<NUM>, <NUM>, ..., 100n), each adapted to be connected to a respective well so as to take up gas from said respective well; a connecting manifold (<NUM>) to which said pipes (<NUM>, <NUM>, ..., 100n) lead; wherein said system comprises first means for individually measuring the percentage of oxygen O<NUM> in the gas transiting in each of said pipes (<NUM>, <NUM>, ..., 100n), characterized in that said system comprises second means for measuring the percentage of oxygen O<NUM> in the gas mixture exiting from said connecting manifold (<NUM>), means for individually adjusting the gas flow in each of said pipes (<NUM>, <NUM>, ..., 100n) as a function of the percentages of oxygen measured by said first measuring means and/or second measuring means, further characterized in that said system comprises a discharge pipe (<NUM>) in connection with said connecting manifold (<NUM>) and adapted to discharge the gas mixture transiting in said connecting manifold <NUM> toward a plant or similar utility, and characterized in that said second means for measuring the percentage of oxygen O<NUM> in the gas mixture exiting from said connecting manifold (<NUM>) comprise a second oxygen sensor (<NUM>) and in that said system (<NUM>) comprises a deviation pipe adapted to deviate part of the gas mixture transiting in said discharge pipe (<NUM>) into said second oxygen sensor.