Piero Pinamonti

Multistage Centrifugal Compressor Surge Analysis: Part II—Numerical Simulation and Dynamic Control Parameters Evaluation

This paper describes, from a theoretical point of view, the behavior of compression systems during surge and the effect of passive and active control devices on the instability limit of the system. A lumped parameter model is used to simulate the compression system described in Part I of this work (Arnulfi et al., 1999), based on an industrial multistage centrifugal compressor. A comparison with experimental results shows that the model is accurate enough to describe quantitatively all the features of the phenomenon. A movable wall control system is studied in order to suppress surge in the compressor. Passive and active control schemes are analyzed, they both address directly the dynamic behavior of the compression system to displace the surge line to lower flow rates. The influence of system geometry and compressor speed is investigated; the optimum values of the control parameters and the corresponding increase in the extent of the stable operating range are presented in the paper.

Optimization of Distributed Trigeneration Systems Integrated with Heating and Cooling Micro-grids

ABSTRACT The article deals with the influence of the amortization period in the optimization of a distributed urban district heating and cooling trigeneration system. The model, presented in detail in [1], is based on a Mixed Integer Linear Program (MILP) and includes a set of micro-cogeneration gas turbines for producing electricity and thermal energy and a set of absorption chillers, driven by cogenerated heat, for producing cooling energy. Micro-gas turbines and absorption chillers can be used instead of purchasing electricity from the grid, producing thermal energy by boilers and cooling energy by compression chillers. Moreover, various building can be connected each other through a district heating and cooling network (DHC network). The optimization specifies the kind, the number and the location of cogeneration equipment and absorption machines, the size and the position of district heating and cooling pipelines as well as the optimal operation of each component. The objective function takes into ac...

Extensive study on the control of centrifugal compressor surge

Abstract This paper reports the results of an extensive study concerning surge instability in an industrial compression system and its dynamic suppression. Both numerical simulations and experiments have been used to analyse the system behaviour under unstable operating conditions and to compare different control devices for surge suppression. First, the characterization of surge is performed over the whole unstable operating range of a compression system based on a four-stage centrifugal compressor. The unsteady energy associated with the surge cycle is employed as an index of the surge intensity to allow for a quantitative approach to the problem. Subsequently, the behaviour and performance of a passive-type control system and of an active-type one are analysed and compared. The former consists of an innovative device based on an oscillating water column, whereas the latter is a high-gain type of feedback device implemented digitally. Experimental data show that the proposed passive device is effective not only in inhibiting surge development, but also in suppressing fully developed instability. The active device turns out to be more effective than the passive one, but under severe conditions it may fail because of actuator limitations and noise amplification. Finally, the relative merits and limitations of the two control systems are discussed with reference to their effectiveness range, flexibility, steady-state performance, installation, maintenance, and costs.

An Innovative Device for Passive Control of Surge in Industrial Compression Systems

The present paper reports a numerical-experimental study on the dynamic behavior of a compression system based on a multistage centrifugal blower and fitted with an innovative device for the dynamic suppression of surge instability. The control device is of passive type and is based on the aeroelastic coupling of the basic compression system with a hydraulic oscillator. The controlled system is modeled at first by using a nonlinear lumped parameter approach. The simulated system dynamics within a wide range of operating conditions allows a parametric analysis to be performed and the optimal values of the control parameters to be singled out. Such optimal values are then used to design the hydraulic oscillator, which results in a technically feasible and very simple configuration. Finally, experimental tests are carried out on the compression plant with and without the passive control device, which demonstrate the effectiveness of the proposed control system in suppressing surge instabilities, at least within the limits predicted by the numerical simulation.

Experimental Evaluation of a High-Gain Control for Compressor Surge Suppression

The present paper considers the suppression of surge instability in compression systems by means of active control strategies based on a high-gain approach. A proper sensoractuator pair and a proportional controller are selected that, in theory, guarantee system stabilization in any operating condition for a sufficiently high value of the gain. Furthermore, an adaptive control strategy is introduced that allows the system automatically to detect a suitable value of the gain needed for stabilization, without requiring any knowledge of the compressor and plant characteristics. The control device is employed to suppress surge in an industrial compression system based on a four-stage centrifugal blower, An extensive experimental investigation has been performed in order to test the control effectiveness in various operating points on the stalled branch of the compressor characteristic and at different compressor speeds. On one hand, the experimental results confirm the good performance of the proposed control strategy; on the other, they show some inherent difficulties in stabilizing the system at high compressor speeds due to the measurement disturbances and to the limited operation speed of the actuator.

Multistage centrifugal compressor surge analysis : Part I. Experimental investigation

This paper reports an experimental investigation on centrifugal compressor surge. The compression system consists of a four-stage blower with vaned diffusers and a large plenum discharging into the atmosphere through a throttle valve. Measurements of unsteady pressure and flow rate in the plant, and of instantaneous velocity in the diffusers of the first and fourth compressor stage, are performed during deep surge, at several valve settings and three different rotation speeds. Additional tests have been carried out on a different system configuration, i.e., without plenum, in order to obtain the steady-state compressor characteristics and to collect reference dato on stall in surge-free conditions. In this configuration, a fully developed rotating stall was detected in the compressor diffusers, while during surge it affects only a limited part of the surge cycle. The goal of the present experimental work was to get a deeper insight into unstable operating conditions of multistage centrifugal compressors and to validate a theoretical model of the system instability to be used for the design of dynamic control systems.

Optimal Lay-Out and Operation of District Heating and Cooling Distributed Trigeneration Systems

The paper deals with the optimization of a distributed urban district heating and cooling cogeneration system. The model is based on a Mixed Integer Linear Program (MILP) and includes a set of micro-cogeneration gas turbines and a district heating network potentially connecting each considered building to all the others. Absorption machines, supplied with cogenerated heat, can be used instead of conventional electrical chiller to face the cooling demand. In addition, a district cooling network can be introduced, independently from the district heating one. The objective of the paper is to obtain the optimal synthesis and operation strategy of the whole system, in terms of Total Annual Cost for owning, maintaining and operating the system. The solution has to specify the kind, the number and the location of cogeneration equipment and absorption machines, the size and the position of district heating and cooling pipelines as well as the optimal operation of each component. The effects of different plant options, comparing cogeneration and tri-generation machines adoption and district heating and cooling pipelines installation, are considered.Copyright

Effect of Different Economic Support Policies on the Optimal Definition and Operation of a CHP and RES Distributed Generation Systems

This paper deals about the application of MILP for economic optimization of complex cogenerative systems. In particular, it optimizes both the size and operating strategy of CHP systems and the lay-out of micro district heating networks applied to a urban contest. The proposed model considers the possible adoption of a set of micro-cogeneration gas turbines located in different buildings, and of a centralized cogeneration system thus allowing part of the required thermal energy to be produced in a single site. In addition, thermal and photovoltaic panels can be integrated into the system to improve thermal and electrical energy production, respectively. Each site can be connected to the others through district heating micro-grids. Hence thermal energy can be distributed inside the system. A further objective of the paper is to evaluate the effect of different economic support policies on the optimal solution, and to relate the economic effort implied in each support policy with the expected results in terms of CO2 emissions reduction and primary energy savings.Copyright

EXPERIMENTAL INVESTIGATION ON ROTATING STALL IN A CENTRIFUGAL BLOWER WITH TWO AND FOUR STAGES AND VANELESS DIFFUSERS

The paper presents the results of an experimental investigation on a multistage centrifugal blower, during rotating stall. The test plant allows to change the turbomachine characteristics; in this research the blower has been tested in two different configurations: two-stage and four-stage, with vaneless diffusers.The unsteady flow field inside the blower has been measured by means of hot-wire anemometers. Three single hot-wire probes have been utilised to measure the development of the rotating stall, while a crossed hot-wire probe has been utilised to obtain the instantaneous flow field behind the impellers.The measurements have been done at different flow rate values, including stall inception.Copyright

Optimization of an Industrial Area Energy Supply System With Distributed Cogeneration and Solar District Heating

The paper presents the optimization of an energy supply system for an industrial area. The system is mainly composed of a district heating network (DHN), of a solar thermal plant with long term heat storage, of a set of combined heat and power units (CHP) and of additional thermal/cooling energy supply machines. The thermal vector can be produced by solar thermal modules, by fossil-fuel cogenerator or by conventional boilers. The optimization algorithm is based on a Mixed Integer Linear Programming (MILP) model and it has to determine the optimal structure of the energy system and the size of the components (solar field area, heat storage volume, machines sizes, etc.). The model allows to calculate the economical and environmental benefits of the solar thermal plant compared to the cogenerative production, as well as the share of the thermal demand covered by renewable energies. The aim of the paper is to identity the optimal energy production mix able to meet the user energy demands and furthermore how the solar thermal energy integration affects the optimal energy system configuration. The average costs of the heat produced for the users have been evaluated for different optimal configurations, and it emerges that the solution including some cogenerators located in strategic production units, the district heating network, the long term heat storage and a solar plant of proper size, allows achieving the lowest cost of the heat. Thus, the integrated solution turns out to be the best from both the economical and environmental point of view.© 2012 ASME