Compressor Controls Corporation

Conocophillips Company

Saul Mirsky

Naum Staroselsky

Wayne Jacobson

Krishnan Narayanan

Brett W Batson

Jeff McWhirter

David J Hoogerwerf

Paul A Reinke

Michael Lev Tolmatsky

Paul F Fisher

John R Wolflick

Serge Staroselsky

Paul Marvin Negley

Boris Zilberman

Vadim Shapiro

Nauman Islam

Robert J Sibthorp

A control method and apparatus for startup of turbocompressors to avoid overpowering a driver of the turbocompressor. In a first embodiment, the control system monitors input signals from transmitters of various control inputs. When the input signals exceed threshold values, the control system begins to close the antisurge valve. In a second embodiment, the antisurge valve begins to close after a predetermined time measured from the time startup is initiated. In both embodiments, the antisurge valve continues to ramp closed until the compressor has reached its operating zone, or until the compressor's operating point reaches a surge control line, at which point the antisurge valve is manipulated to keep the compressor from surging.

Enhanced turbocompressor startup

A control method and apparatus for critical rotational speed avoidance in a compressor-expander set in a gas refrigeration system. By varying an opening of an antisurge or recycle valve, a shaft power used by the compressor in the compressor-expander set may be varied, thereby varying the rotational speed of the compressor-expander set to move it away from its critical speed zone. Additionally, a feedforward signal may be provided by a compressor-expander set control system to cause an antisurge valve for a recycle compressor to open upon a trip or shutdown of one compressor-expander set.

Compressor-expander set critical speed avoidance

A control method and apparatus for simultaneously protecting a compression system from driver overpowering and turbocompressor surge. When overpowering is detected, flow rate through the each compressor in the turbocompressor train is reduced by closing an inlet throttling valve at the inlet of each respective compressor stage unless a compressor operating point is sufficiently near surge. In this latter case, the inlet throttling valve is not closed. In this way, overall flow rate through the compressor train is reduced while maintaining adequate flow through compromised stages to avoid surge.

Compressor-driver power limiting in consideration of antisurge control

Often, an application or process calls for multiple pumps operating within a piping network. Pump load, such as flow rate or pressure, is shared between these multiple pumps. The present disclosure relates to effective means of distributing the pumping load in a manner that satisfies the process requirements while keeping the pumping machinery safe from functioning in damaging operating regions. It also discloses a method of operating pumps in an efficient or optimal fashion. An additional aspect is a method of using an open-loop response to deal with large transients threatening to force a pump into an operating region that might result in damage or destruction.

Controlling multiple pumps operating in parallel or series

Accurate and effective antisurge control for turbocompressor stages is augmented by measuring the flow rate of fluid entering or leaving the stage of compression. On the other hand, turbocompressors with sidestreams, such as ethylene, propylene, and propane refrigeration compressors, pose unique antisurge control challenges; in particular, measurements for the flow rate entering (or leaving) the compressors' middle stages are not available in most cases. Furthermore, the methods used to cope with this lack of flow measurements are prone to introducing errors and producing false transients, as well as being cumbersome and difficult to implement. For these reasons, this disclosure relates to a method for protecting turbocompressors with sidestreams from the damaging effects of surge. But more specifically, it describes a technique for estimating the reduced flow rate entering a compression stage not having a flow measurement device in its suction or discharge&mdash;that is, the flow rate entering a middle (intermediate) compressor stage can be inferred from known flow rates. The reduced flow rate is used to determine a location of the compression stage's operating point relative to its surge limit. The proposed method employs (1) the first law of thermodynamics to estimate the temperature of a flow entering one of the compressor stages, and (2) a relationship between the pressures and temperatures in suction and discharge used in conjunction with the first law of thermodynamics.

Method and apparatus for estimating flow in compressors with sidestreams

An objective in a natural gas liquids (NGL) plant is that of achieving and maintaining maximum productivity. If this plant is equipped with a turboexpander that drives a gas compressor (recompressor), maximum turboexpander productivity provides maximum plant productivity attained by maximum compressor power. This is accomplished by manipulating the compressor operating point location (by adjusting the opening of the antisurge valve) and by controlling rotational speed. The subjects of the proposed invention are the method and apparatus (comprising a turboexpander/recompressor rotational speed controller and a recompressor antisurge controller) providing maximum turboexpander/recompressor rotational speed and recompressor operating point location (corresponding to maximum power) by opening the turboexpander's adjustable nozzles and the recompressor antisurge valve.

Method and apparatus for maximizing the productivity of a natural gas liquids production plant

This invention discloses a method for limiting a critical variable (such as, discharge pressure or suction pressure or pressure ratio) of either a compressor station or an individual compressor when these machines are subjected to large, fast disturbances. Each configuration, whether a station or an individual compressor, is equipped with two PID controllers: (1) a main controller for compressor critical variables and (2) a limiting controller that participates in modulating recycle valves. At the onset of sudden, large changes of mass flow at a compressor's or station's discharge, the effectiveness of the two controllers (acting independently) may be insufficient to prevent discharge pressure from reaching the shutdown set point which, in turn, disrupts the process supported by the compressors, and the longevity of the drivers is diminished. For these reasons, this disclosure relates specifically to a technique that combines the functions of the main and limiting controllers. Because of the complementary (synergistic) interaction of the controllers, an earlier and faster opening of the antisurge valves is initiated, and pressure at the discharge header is effectively limited.

Method and apparatus for limiting a critical variable of a group of compressors or an individual compressor

The operation of quickly taking a turbocompressor off-line from a parallel configuration, of a gas pipeline compressor station, may encounter increased mechanical action (in particular, vibration) upon recycle piping and the additional risk of compressor surge. For these reasons, this invention relates to a method and apparatus for decreasing vibratory loads and for increasing surge prevention effectiveness, while initiating an off-line operation, by (1) altering the surge control line's location, at a preset rate, from its initial location to a predetermined new location; and (2) decreasing the turbocompressor's deceleration rate when the operating point intercepts the surge control line before the control line reaches its new location. Upon completion of the off-line activity, the control line returns to its initial location; and the reduction of compressor speed will cease on reaching a preset value.

Method and apparatus for preventing surge while taking a turbocompressor

The stroking speed of an antisurge control valve is impeded by the combined damping effects of signal dead time and the inherent lag of ancillary pneumatic components within a primary control loop. Furthermore, as control valve actuator size increases, the negative influence of these two impediments (dead time and lag) is amplified. As a result, control valve response times are adversely affected; and the possibilities of surge-induced compressor damage and process upsets are heightened. For these reasons, this disclosure relates to a method for protecting turbocompressors from impending surge, and for preventing subsequent process upsets, by improving antisurge control. But more specifically, it describes a technique for decreasing damping effects by evacuating control valve actuators (diaphragm or piston) through restrictions having a lower resistance to compressible-fluid flow rather than through volume boosters--consequently, increasing a control valve's opening speed to that of an emergency shutdown. The proposed method (1) allows continuous control of antisurge control valves and (2) incorporates both solenoid valves and quick exhaust valves (located adjacent to the actuators) which are manipulated by predefined discrete signals from antisurge controllers.

Method and apparatus for improving antisurge control of turbocompressors

A method is provided for controlling fuel flow to the combustor of a gas generator turbine during sudden changes in load or during a surge cycle of the process turbocompressor. Surge control is initiated by analog input signals emanating from various devices located throughout the compressor-process system. The fuel control system includes input signals from the gas turbine driver. These signals are acted upon by the fuel control system which transmits a signal to a fuel valve actuator that controls the valve that meters fuel to the combustor. In addition to this sequence of control communication, however, is a rate-of-change in the amount of the fuel provided. The rate of the increase of the amount of fuel is determined by current operating functions of the fuel control system. However, because of the characteristics of general load rejection and recovery, and the abrupt nature of surge, the rate of change in the flow rate of fuel is extremely high. This rapid increase of fuel to the combustor may lead to dangerous excursions in temperature, resulting in high temperatures in gas turbine elements. Consequently, a new function is added to the fuel control system's operation whereby improved regulation of the rate of increase of fuel is achieved. This new function receives a signal that either surge or a change in load has been detected. Next, a signal is transmitted to the fuel valve actuator, regulating fuel to the combustor, thus power to the power turbine, thereby preventing overspeeding. After that, the rate of change of the fuel valve is limited for a period of time. Once recovery has been accomplished, the change rate of the fuel valve is gradually returned to a normal operating setting.

Prevention of parameter excursions during process compressor surge in

An improved method is provided for controlling fuel flow to the combustor of a gas generator turbine during sudden changes in load or during a surge cycle of the process turbocompressor. Surge control is initiated by analog input signals emanating from various devices located throughout the compressor-process system. The fuel control system includes input signals from the gas turbine driver. These signals are acted upon by the fuel control system which transmits a signal to a fuel valve actuator that controls the valve that meters fuel to the combustor. In addition to this sequence of control communication, however, is a rate-of-change in the amount of the fuel provided. The rate of the increase of the amount of fuel is determined by current operating functions of the fuel control system. However, because of the characteristics of general load rejection and recovery, and the abrupt nature of surge, the rate of change in the flow rate of fuel is extremely high. This rapid increase of fuel to the combustor may lead to dangerous excursions in temperature, resulting in high temperatures in gas turbine elements. Consequently, a new function is added to the fuel control system's operation whereby improved regulation of the rate of increase of fuel is achieved. This new function receives a signal that either surge or a change in load has been detected. Next, a signal is transmitted to the fuel valve actuator, regulating fuel to the combustor, thus power to the power turbine, thereby preventing overspeeding. After that, the rate of change of the fuel valve is limited for a period of time. Once recovery has been accomplished, the change rate of the fuel valve is gradually returned to a normal operating setting.

Prevention of parameter excursions in gas turbines

Balancing the load between compressors is not trivial. An approach is disclosed to balance loads for compression systems which have the characteristic that the surge parameters, S, change in the same direction with rotational speed during the balancing process. Load balancing control involves equalizing the pressure ratio, rotational speed, or power (or functions of these) when the compressors are operating far from surge. Then, as surge is approached, all compressors are controlled, such that they arrive at their surge control lines simultaneously.

Method and apparatus for load balancing among multiple compressors

A method and apparatus are disclosed for protecting gas turbines (two- and three-shaft) from damage or destruction during dangerous transients. In this situation, fuel flow must be reduced, as needed, to keep the exhaust gas temperature below a maximum limit, thereby avoiding damage to blading in the turbine's first-stage. The dynamic action of the temperature downstream of the combustion chamber may be estimated and then used to correct the temperature measured by thermocouples. For this approach, the turbine is instrumented with an inlet pressure transmitter and an outlet temperature transmitter. The method dynamically estimates temperatures downstream of the combustion chamber and reduces the fuel flow rate if the estimated temperature approaches the temperature limit. Existing thermocouple measurements (EGT) are used as well as the pressure of air exiting the compressor (CDP) upstream of the combustion chamber. By employing a first-order lag and a steady-state gain, the measured CDP is used to predict a 'correction' EGT signal which is then added to the measured EGT, resulting in a corrected EGT. Once the corrected EGT has been calculated, its first time-derivative is used to adjust the safety margin between a maximum allowable limit temperature and a lower predetermined temperature set point.

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West Des Moines, IA, United States of America

Saul Mirsky