Abstract: A domestic hot water heating system which disables the normal aquastat during set-back periods where the temperature of the water source is sensed at the output manifold and the temperature of the water also is sensed a predetermined distance along the manifold to determine a demand or lack of demand for hot water. The system will enable the aquastat during a set-back period when demand is made and disable the aquastat when there is no longer a demand.

Abstract: The invention concerns a control device for gas boilers. The overall functions involving control and safety are ensured by a control box (26) with microprocessor which centralizes data collected from the ambient thermostat (27), the temperature sensor (28) on the duct (21) for heating water return, the air output sensor (19), the drawing contact (31), the extraction fan (6) speed sensor (30), and the lighter (24), and it converts them into digital signals that are made to operate the lighter, the circulation pump (19), the gas inlet electrovalve (12) and the extraction fan according to the control data that the microprocessor has memorized. Application for forced draft steamtight gas boilers.

Abstract: Controlling a fluidized bed coal combustor by sensing certain variables and thereby controlling other variables.

Abstract: A desired ratio of offgas to fuel gas is maintained for a fuel mixture supplied to the burners associated with a boiler by venting steam as required to insure than all offgas may be combusted while maintained the desired offgas to fuel gas ratio. The venting of steam causes the fuel gas control, which is based on steam pressure, to vary the flow rate of the fuel gas so as to maintain the desired offgas-fuel gas ratio. Control of the combustion process for the boiler in this manner results in total combustion of the offgas without violating process constraints.

Abstract: The control of the actual liquid level in a boiler is accomplished by using the flow rate of the fuel to the combustion system associated with the boiler to generate a signal which is utilized to bias a control signal generated in response to steam flow rate and the output from a conventional level controller in such a manner that swell and shrink caused by changes in fuel flow rate is compensated for and the desired liquid level is maintained in the boiler.

Abstract: A once-through steam generator has both radiant and convection sections. The flue gases discharged from the convection section are passed through a wet scrubber to remove both sulfur oxides (SO.sub.x) and particulate matter. The feedwater to the convection section has its temperature controlled by the temperature of the flue gases discharged from the convection section, reducing the temperature of the feedwater by the use of a feedwater exchanger, as the convection section progressively fouls due to particulates in the flue gases. An additional heat exchanger upstream of the feedwater exchanger and convection section which scavenges additional heat from the wet scrubber liquids while the temperature of the flue gases into the scrubber are lowered to a temperature equal to or less than the water dew point temperature of the flue gases entering the scrubber.

Abstract: A combustion control apparatus of a combustion furnace by an improved fuel and air complementary control system according to master control system is disclosed, which is provided with a regulating means connected to a master controller and adapted for detecting the amount of load change and for setting the length of an air damper control rod's length changing device to a preset standard value corresponding to the load, without controlling the oxygen concentration in the exhaust gas to a standard value, when the load change is increased to a value of not lower than the preset value. The combustion control apparatus can control stably the oxygen concentration in an exhaust gas to a low level even when a load is suddenly changed.

Abstract: The control of the actual liquid level in a boiler is accomplished by using the actual enthalpy of the fluid in the boiler to generate a signal which is utilized to bias the output from a conventional level controller in such a manner that swell and shrink causes by disturbances is compensated for and a desired liquid level is maintained in the boiler.

Abstract: An improved control system and method for maintaining the outlet temperature of a process fluid exiting from a process fluid coil located in the convection section of a boiler having a convection section and a radiant section. The improved control system and apparatus comprise means for measuring the inlet temperature and the flow rate of a process fluid to the process fluid coil and means for measuring the temperature of the process fluid at the outlet of the process fluid coil. The improved control method and apparatus also comprise a first means responsive to changes in the inlet temperatures and flow rate to vary the amount of flue gas recirculated from the convection section of the boiler to the radiant section and a second means responsive to changes in the outlet temperature of said process fluid to vary the amount of fuel feed to the combustion section of said boiler.

Abstract: The efficiency of a furnace is substantially maximized by manipulating the amount of oxygen supplied to the combustion process in the furnace so as to provide a desired oxygen concentration in the flue gas which will result in substantially maximum furnace efficiency. Feed forward control based on the fuel flow rate may also be utilized to enable the control based on oxygen concentration in the flue gas to respond more quickly to a change in the fuel flow rate.

Abstract: A control apparatus for controlling the generators of a multiple steam generator or multiple hot water generator installation. The control apparatus includes burner command apparatus which limits each of the generators to one of at least two different maximum firing rate levels. The command apparatus is controlled by a data storage device, such as a microcomputer, which periodically adjusts the maximum firing rate level of the generators in accordance with the predicted loads of the installation. The firing rate of the generators is controlled by modulating apparatus which varies the firing rate within the maximum firing rate levels in accordance with the actual measured installation load. By controlling the actual firing rate in response to both the predicted and the actual installation loads, efficiency of operation may be optimized.

Abstract: A pressure control system for an air distribution system which includes a supply blower (10), a distribution duct network (20) and a plurality of air outlets (22a, 22b), includes a plurality of pressure sensors (25a, 25n) positioned at various points in the air ducts to measure pressure therein. Controls are provided for selecting the lowest of the sensed pressures (42) and the low pressure signal becomes one input to a variable dead band controller (44). Another input is an adjustment (45) for commanding the desired system pressure. The controller compares the pressure to a dead band threshold established about the set point and delivers appropriate signals to an actuator (31) which operates through a linkage (32) to control the inlet vortex vanes (33) and hence the air flow of the supply blower. A wide dead band is used to avoid hunting of the system, but when a response is required a narrow dead band is used to ensure that the system drives to the set point.

Abstract: A method and system for controlling the combustion of, for example, coal or bark in a stoker boiler or black, liquor in a recovery boiler to provide operation at maximum efficiency. Control loops are provided for primary or undergrate air and secondary or overfire air. The undergrate air control loop is adjusted as a function of carbon dioxide or steam/fuel ratio, and the overfire air control loop is adjusted as a function of carbon monoxide. In addition to carbon monoxide, combustibles and opacity may be used. Air redistribution is also used to minimize combustibles or CO or opacity.

Abstract: A boiler control system for boilers fired by solid fuels wherein the fuels are carried through the combustion zone of the boiler on a traveling grate and wherein the air flow for combustion as supplied to the undergrate region utilizes a control of the fuel rate from a deviation of the outlet pressure from the desired value with the control of the air flow to the undergrate region maintained generally in proportion to the steam flow from the boiler with the proportionality being biased from the deviation of the outlet pressure from its desired value.

Abstract: Apparatus is provided for constructing an induced draft furnace and its control system, to produce an induced draft furnace having increased efficiency. A blower located in the furnace exhaust stack is used to induce movement of air, fuel and combustion products into, through and out of the combustion chamber. A flow-limiting orifice in the exhaust stack in proximity to the blower causes a region of higher pressure to exist upstream from the orifice, with a region of lower pressure downstream from the orifice. A pressure signal representative of the flow rate of exhaust stack gases is sensed on one side of the orifice and is fed back to a modulating gas valve which controls the outlet gas flow from the valve to be proportional to the magnitude of the pressure signal representing exhaust stack flow rate. By selecting blower speeds and flow capacities, various firing rates for the furnace can be selected, from the design maximum of the furnace down to various derated levels.

Abstract: Boiler outlet temperature in a sliding pressure operation is controlled in a routine way by varying the fluid or heat distribution in the boiler. The effect a change in pressure has on steam temperature is anticipated by supplying a feedforward signal to the temperature control system from drum pressure so as to minimize temperature variations at the boiler outlet.

Abstract: Apparatus controlling a plurality of fuels of different heat contents to a fluid heater burner including valves for selectively connecting the fuels to the burner and pressure responsive fuel flow regulators responding to the combined fuel/air pressure at the fuel burner to provide a given level of output for the boiler.

Abstract: Measurements of the instantaneous flow of heat delivered to the vapor generator and the quantity of vapor flowing momentarily through the contact heating surface are made and the resultant signals are compared by subtraction or division to obtain a comparison signal. The comparison signal is then imposed on a control element in the form of a valve to cause an injection of more or less water into the vapor flowing into the heating surface in order to regulate the exit temperature of the vapor.

Abstract: A plurality of first logic processors are interconnected in a "ring" type network and individually exercise control over similar equipment group subsystems which individually contribute to the operation of an overall system. Each of the interconnected processors, in addition to its primary control function, monitors the safety of operation of the equipment group with which associated and the safety of operation of a "neighboring" equipment group. Redundant safety checks are thus performed on each equipment group and any discrepancies in the results of such safety checks are enunciated. A pair of further logic processors, in addition to performing other control functions including scheduling the operation of the individual equipment groups, redundantly check the safety of operation of the overall system.

Abstract: A furnace draft control for a fossil fuel fired steam generator wherein the rates of flow of fuel, air and flue gas are adjusted in parallel in accordance with changes in power demand and the forced and induced drafts are adjusted in opposite directions as required to maintain furnace draft at set point.

Abstract: This invention is an automatic control system, for example, for controlling the burner in a boiler in accordance with changes in the desired or actual steam demand and the invention is an improvement on the subject of British Patent Specification No. 1084671 which was for one system for automatically adjusting the air and fuel supplies in accordance with changes in the measured steam pressure or the demanded steam pressure.