TWI507643B - Regenerative air preheater design to reduce cold end fouling - Google Patents

Description

Regenerative air preheater capable of reducing cold end fouling

The present invention generally relates to a vapor generation system having a fossil fuel combustion boiler and a regenerative air preheater. More specifically, the present invention relates to a vapor generation system having a fossil fuel fired boiler and a rotary regenerative air preheater exhibiting reduced fouling during various boiler operating levels.

During the combustion of the boiler, the sulfur in the fuel is oxidized to SO ₂ . After the combustion process, some amount of SO ₂ is further oxidized to SO ₃ , and typically about 2% to 2% of SO ₂ will become SO ₃ . Iron oxide, vanadium and other metals are present at a suitable temperature range to produce this oxidation. Selective catalytic reduction (SCR) is also well known to oxidize a portion of the SO ₂ in the flue gas to SO ₃ . The catalyst formulation (primarily the amount of vanadium in the catalyst) affects the amount of oxide and the oxide ratio is from 0.5% to over 1.5%. More typically about 1%. As a result, a significant increase in SO ₃ emissions can be observed in power plants that burn high-sulfur coal with new SCRs, which can result in visible smoke, local acid ground level problems, and other environmental issues.

Rotary regenerative heat exchangers are commonly used on large fossil fuel fired boilers to transfer hot self-heating flue gas to cooler input air provided to one of the boiler's combustion chambers. This type of heat exchanger is generally referred to as an air preheater. The purpose of using an air preheater is to increase the efficiency of a fossil fuel fired boiler. Basically, a rotary regenerative air preheater consists of a large cylinder encased with a plurality of spaced apart metal sheets. The sheets are separated from each other to allow a hot flue gas stream to pass over the surface of each of the plates parallel to the axis of the cylinder to heat the sheets. The hot sheets are rotated to a cooler input air stream to heat the input air. The flue gases and input air generally flow through the air preheater in opposite directions. The entire cylinder is continuously rotated about its axis such that the hot and cold air flows alternately through the same metal sheet.

The product of the combustion of fossil fuels usually contains both sulfur trioxide (SO ₃ ) and water vapor (H ₂ O), so when the exhaust gas is cooled to a sufficient extent in the air preheater, SO ₃ and water vapor Combined and condensed into liquid sulfuric acid (H ₂ SO ₄ ). This occurs when the temperature of the surface (such as the heat exchange element of an air preheater) is below the dew point of sulfuric acid. When both the ash particles and the sulphuric acid are deposited on the metal surface in the air preheater, they are bonded to the metal surfaces and cause a phenomenon called scale. Since fouling limits the amount of air and gas flowing through the air preheater, the efficiency of the air preheater is reduced.

High velocity vapor jets or air jets are periodically directed to the metal surfaces to remove dust/acid deposits during what is known as sootblowing. Soot blowing removes some but not all deposits from the metal sheets.

The cold end of the regenerative air preheater is generally in line ₂ SO below the dew point of the flue gas of H _4, so that a portion of the condensed H ₂ SO ₄ in such heat exchange surface of the element. As the condensed dust and H ₂ SO ₄ aggregate, it causes a pressure drop to build up in the flow through the heat exchanger 100. Since solids such as dust and other solid materials from the combustion of the fuel also accumulate on the heat exchange elements, the pressure drop will become greater over time. If the fouling is sufficiently severe, the flow path between the metal sheets may be blocked. In this case, the heat transfer surface area is lost and the fan may not be able to move the necessary amount of combustion air through the air preheater.

The cold end of the air preheater has a higher gas density and therefore a lower flow rate due to one of the lower gas temperatures. In general, the cold end flow rate is only about 60% of the hot end flow rate. Lower gas flow rates also result in more fouling.

There are also other factors that increase fouling, such as low boiler loads. The low boiler load causes this speed to drop to as low as 25% of the hot end maximum continuous rating (MCR).

There is a need for an air preheater that is resistant to fouling under a variety of combustion conditions.

Briefly, one preferred form of the invention is an air preheater that is more resistant to "fouling" under various boiler loads.

It is an object of the present invention to provide an air preheater that is more resistant to corrosion.

It is an object of the present invention to provide an air preheater that can be adjusted for various boiler loads.

It is an object of the present invention to provide an air preheater that can adjust the flue gas velocity under various boiler loads.

Other objects and advantages of the invention will be apparent from the description and drawings.

The invention will be more fully understood and appreciated by the appended claims appended claims.

Most steam generation systems utilize static or rotary regenerative air preheaters to increase boiler efficiency. The most common type is a rotary regenerative air preheater. This type of air preheater is characterized by a rotating heat exchange element. This invention relates to a boiler system equipped with any type of regenerative air preheater. To facilitate the discussion, the configuration of the present invention will be discussed in connection with a rotary regenerative air preheater.

Referring to Figure 1 of the drawings, a conventional rotary regenerative preheater 100 is shown. The air preheater 100 has a rotor 112 that is rotatably mounted in a housing 114. The rotor 112 is formed by a diaphragm or partition 116 extending from a rotor post 118 to a periphery of the rotor 112. The partition 116 defines a compartment 120 therebetween for securing the heat exchange element basket assembly 122.

In a typical rotary regenerative heat exchanger 100, a flue gas stream 224 and a combustion air inlet stream 230 enter the rotor 112 from opposite ends and are disposed in opposite directions over the heat exchange element basket assembly. Heat exchange element 142 within 122. Thus, the cold air inlet 130 and the cooled flue gas outlet 126 are located at one end of the heat exchanger, the end being referred to as the cold end 144, and the hot flue gas inlet 124 and the heated air outlet 132 are located in the air pre- The opposite end of the heater 100, which is referred to as the hot end 146. Segment plate 136 extends across the housing 114 adjacent the upper and lower faces of the rotor 112. Segment plate 136 divides air preheater 100 into an air section 138 and a flue gas section 140.

The arrows of FIG. 1 indicate the direction of flue gas flow 224 and air flow 230 through the rotor 112. The flue gas stream 224 entering through the flue gas inlet 124 transfers heat to the heat in the heat exchange element basket assembly 122 mounted in the compartments 120 positioned in the flue gas section 140. Exchange element 142. The heated heat exchange element 142 is then rotated to the air section 138 of the air preheater 100. The heat stored by the heat exchange element basket assembly 122 is then transferred to the air stream 230 entering through the air inlet 130. The cold flue gas outlet stream 226 exits the preheater 100 through the flue gas outlet 126 and exits the preheater 100 through the heated air outlet stream 232.

As noted above, the additional acid build-up of the cold end 144 of the air preheater 100 creates a large pressure drop across the air preheater 100. The particulate matter carried in the flue gas also accumulates on the surface of the heat exchange elements 142 over time, and the presence of such deposits increases the pressure drop of the air preheater. This particulate matter tends to concentrate primarily in localized areas with low flow rates.

Therefore, fouling is attributed to two problems: (1) condensation of acid that collects fly ash and other particles; and (2) areas with low flow rates become lower at low boiler loads.

Attempts have been made to overcome various problems in a variety of different ways. A device is used to only partially block the flue gas inlet. The effect of this device is disappointing. At that time, it did not recognize and solve all the factors that caused the scale.

The present invention addresses acid condensation problems and speed-related fouling problems. High velocity particle streams erode solid materials during one of the processes similar to sand blasting. erosion The rate is proportional to the rate of increase to more than one power. My experience is that fly ash erosion is proportional to the flow rate that increases to 3.4 volts.

Therefore, it is beneficial to increase the flow rate in the gas section to reduce the amount of deposition on the heat exchange elements 142. Increasing the flow rate in the air section does not advantageously assist in the removal of deposits because there is little or no particulate matter in the gas section. However, reducing the amount of heat transfer surface in the gas section does have an effect on raising the temperature of the gas in the gas section, which results in less acid condensate and therefore less fouling.

The air flow entering the boiler is related to the operating level of the boiler. Therefore, a boiler operating at 60% of its maximum continuous rating (MCR) would require and consume less combustion air than the same boiler operating at 90% of the MCR. Therefore, boilers operating at 60% MCR have less flue gas than boilers operating at 90% MCR. The less the amount of flue gas having about the same density exiting through the same cross section, the lower the exit velocity.

At the same time, when the boiler is operated at 60% MCR relative to 90% MCR, it produces a flue gas that exits the lower temperature. Therefore, the boiler operating level affects the input air velocity entering the boiler, the exit flue gas flow rate exiting the boiler, and the temperature exiting the flue gas.

Referring to Figure 2, the present invention includes baffle assemblies 152, 162 adjacent the inlet of the air preheater 100. These are attached as close as possible to minimize leakage between the baffle assemblies 152, 162 and the air preheater 100. A controller 158 can be used to partially close the baffle assemblies 152, 162 during reduced boiler load conditions. This effectively reduces the flow area and thus increases the flow rate.

By limiting the flow into both the flue gas inlet 124 and the air inlet 130 of the air preheater, a smaller effective area for heat transfer will result in less heat exchange. This causes a greater portion of the metal surface to have a temperature above the dew point of the sulfuric acid, thereby reducing fouling of the metal surfaces. At the same time, the flow rate in the gas section increases, which promotes erosion of any aggregated deposits.

In addition, if the cold air flowing into the air preheater is heated by another heat exchanger to keep the metal temperature higher than the acid dew point, the air side and the flue gas side of the air preheater 100 are blocked. The flow of heat from the other heat exchangers will be reduced. This will save overall energy because the amount of energy required to block a portion of the metal surface on the air side is less than negligible than the amount of energy required to heat the cold air to a sufficient extent.

2 is a schematic illustration of a vapor generation system having a regenerative air preheater configuration in accordance with the present invention. The system includes a flue baffle assembly 152 positioned inside the hot flue gas inlet 124 as close as possible to the face of the component basket assembly 122. A flue gas duct 154 connects the boiler 148 to the air preheater 100. The baffle of the flue gas baffle assembly 152 (156 of Figure 3) can be closed under reduced load conditions to effectively reduce the flow area of the flue gas inlet 124. This increases the velocity of the flue gas flowing through the heat exchange elements 142. This also reduces the effective surface area used to transfer heat from the flue gas.

The system also includes an air baffle assembly 162 positioned at the preheater cold air inlet 130 as close as possible to the face of the components in the basket assembly 122 to minimize air leakage. The air baffle assembly 162 can be partially closed under reduced load conditions of the boiler 148 to effectively The flow area of the air inlet 130 is reduced and thus the effective surface area for transferring heat to the air flowing into the air preheater 100 is reduced. This means that the cooling of the cold end of the preheater 100 (144 of Figure 1) is reduced.

The fly ash carried in the flue gas erodes the deposit on the surface of the heat exchange element 142 in the air preheater 100 due to the increased flow rate of the flue gas section (140 of Figure 1). The rate of erosion is proportional to the speed that is raised to the specific power of the etchant. For fly ash, this power is 3.4.

Additionally, since the surface area used to extract heat from the flue gases is reduced, the flue gas passing through the air preheater to the cold end is hotter and thus one of the plates in the cold end is larger The percentage is maintained above the H ₂ SO ₄ dew point. This results in less H ₂ SO ₄ condensing on the heat exchange elements (142 of Figure 1).

A controller 158, preferably a programmable logic controller (PLC) having pre-program control logic, monitors the load of the boiler 148 and controls actuation of the baffle blades in the baffle assemblies 152,162.

In a preferred embodiment, the controller 158 receives a signal from a power plant distributed control system (DCS) 160. The DCS 160 can determine the operational load of the boiler 148 based on the monitored parameters and can be programmed to send a signal indicative of the boiler load to the controller 158. Upon receiving the signal, the controller 158 will calculate the boiler load and actuate the baffle assemblies 152, 162 accordingly.

Referring now alternately to Figures 1 and 2, the temperature at a plurality of locations within the air preheater can be monitored. If any structure (temperature) within the flue gas section 140 falls below the dew point of the various acids in the flue gas, the liquid acid condenses on the structures. The liquid acid accumulates and holds the fly ash to accelerate the air preheating The dust of the scale of the device. Typically, the flue gas outlet 126 has the lowest temperature of the flue gas section 140 and is most prone to acid condensation. Accordingly, the controller 158 will receive the temperature reading and determine if the flue gas inlet should be closed more than the flue gas flow rate, thereby reducing the surface area of the exchange element 142 that is exposed to the flue gases. The combination of increased flue gas velocity and reduced heat exchanger surface area reduces the heat taken from the flue gases, thereby increasing the temperature of the flue gas stream 226 exiting the air preheater 100.

Similarly, as the air baffle assembly 162 more closely closes the air inlet 130, the velocity of the inlet air flow 230 increases. Further closing the air inlet 130 also reduces the surface area of the heat exchange elements 142 exposed to the air inlet stream 230. This results in a reduction in the heat absorbed by the air inlet stream 230, again causing the flue gas stream 226 to have a higher temperature exiting the air preheater.

The increase in velocity of the flue gas passing through the air preheater 100 tends to erode deposits accumulated in the air preheater at a rate that increases to a power of 3.4 based on the speed. The controller can operate the flue gas baffle 152 and the air baffle 162 to maximize erosion of the aggregates, however, the baffle assemblies may not be closed until the flue gas allowed to exit exceeds a maximum The degree of temperature allowed. This temperature may be predetermined based on the maximum temperature that the downstream equipment can safely tolerate plus the desired safety margin.

Referring to FIGS. 3-6, the air baffle assembly 162 includes a frame 182 and a plurality of baffles 156 positioned within the frame 182. Preferably, the baffles 156 are grouped into a plurality of baffle panels 163, 164. In addition to the associated baffle 156, each of the blocking panels 163, 164 includes an actuator 166 and a driver 168, which connects the actuator 166 to each of the baffles 156.

As shown in FIG. 3, the air baffle assembly 162 can divide the flue gas inlet (124 of FIG. 2) into segments. The baffles 156 of the baffle sections 163, 164 are positioned to control the flow within the flue gas inlet 124. The other section 174 of the flue gas inlet 124 remains open without a baffle assembly or baffle.

The flue gas baffle assembly 152 has the same components as the air baffle assembly 162 described above and operates in the same manner. Thus, the above description applies equally to the flue gas baffle assembly 152 when applied to the flue gas inlet rather than the air inlet.

The controller 158 operates the actuators 166 of the baffle sections 163, 164 to partially limit the flow in a particular region of the flue gas inlet (124 in Figure 2).

It should be understood that the regenerative air preheater 100 in accordance with the present invention may include more or fewer baffle assemblies 152, 162 as in Figures 3-6. In addition, the smaller or larger portion of the flue gas inlet 124 remains without the baffle assembly to control flow through the flue gas inlet 124.

Figure 6 is an enlarged view of a portion of Figure 5. The display baffle 156 is rotatable about an axis 176 between an "open" position and a "closed" position. A flat rod seal 178 is mounted to both sides of each baffle 156. A rod seal 178 covers and contacts a portion of the rod seal 178 adjacent the baffle to prevent flue gas from flowing between the baffles. A rod seal 178 of the baffle that is closest to the frame 182 contacts a portion of the frame 182 to prevent flue gas from flowing between the frame 182 and the baffle 156.

Referring now to Figure 3, for a vertical flow air preheater, the controller (Figure 2 158) Periodically opening a baffle 156 of a "closed" baffle panel 163 while simultaneously closing the baffles 156 of an "open" baffle assembly 164 while maintaining a substantially constant flow area. This operation allows the baffle 158 of the "closed" baffle assembly 164 to flow out of any dust deposits that may collect on top of the baffles 156.

Referring now to Figure 2, limiting the flow region of the flue gas inlet 124 increases the velocity of the flue gas stream, thereby causing fly ash carried in the flue gas to erode cold end deposits. However, for heat transfer, higher speeds and smaller areas will result in temperatures above the normal flue gas outlet temperature. That is, portions of the closed flue gas inlet effectively block flue gas flow through portions of the installed heat exchange element (142 of Figure 1), thereby reducing the effective heat transfer area and increasing the exit of the air preheater 100. Flue gas temperature.

In addition, a large pressure drop at 100% power requires higher cost for higher pressure air and flue gas fans 188 and higher operating costs for larger motors operating such larger fans 188. In addition to the worst coal, the power plant data measurement system does not show a pressure drop between the soot blowing cycles over a full load of more than 8 hours. The observed fouling is hot end fouling that has formed on some of the hotter upstream surfaces, is propelled by the flue gas stream and carries large particles or slag from "popcorn", or may be Cold-end fouling of acid deposits and/or particulate deposits in low velocity and low turbulence areas.

However, under low load conditions, the gas outlet temperature is always below the gas outlet temperature for the MCR design point. This is due to two factors. Under smaller boiler load conditions, the temperature of the flue gas entering the air preheater 100 is lower than the temperature at the design point. The air preheater 100 is also more efficient because the flue gas velocity is also lower and thus the resulting thermal transfer coefficient has a smaller effect than the flow exiting the surface area, so the temperature in the flue is A greater reduction in degrees. Generally, lower temperatures occurring at low loads are sufficiently low to cause condensation of sulfuric acid. Some power plants use steam heating to increase the inlet air temperature and therefore exit the gas temperature and component plate temperature to avoid condensation of the acid. However, dust accumulation due to reduced speed is not alleviated by this procedure.

Table 1 compares the flue gas velocities of the present invention relative to conventional air preheaters during thirty (30%) load conditions, seventy percent (70%) load conditions, and MRC. The baffle assemblies 152, 162 in accordance with the present invention are used to effect a fifty percent (50%) reduction in the flow area of the flue gas inlet to produce a significant increase in the velocity of the flue gas stream. As can be seen in the table, doubling the inlet velocity of the flue gas doubles the exit velocity of the flue gas and increases the average flue gas exit velocity proportionally to 3.4. Using the present invention, the ratio of the average flue gas exit velocity can be reached to 3.4 volts with 70% power and an MCR of 3.54, using a conventional air preheater, which is 0.32. At a power level of 30%, the ratio of the present invention is 0.43, compared to 0.04 for a conventional air preheater. At 30% load, closing the additional baffle 56 will provide a higher cold end speed and better cleaning (speed to 3.4 volts). The conditions of this example are not necessarily the best conditions, but merely illustrate the principles of the invention.

In alternative embodiments, the baffles can be actuated by a gear drive, a belt drive, a chain mechanism, a solenoid, or other known actuator mechanism. These are all within the scope of the invention.

While the preferred embodiment has been shown and described, various modifications and Accordingly, the invention is to be considered as illustrative and not restrictive.

100. . . Air preheater

112. . . Rotor

114. . . case

116. . . Partition or diaphragm

118. . . Rotor column

120. . . Compartment

122. . . Heat exchange component basket assembly

124. . . Hot flue gas inlet

126. . . Heated air outlet

130. . . Air inlet

132. . . Air outlet

136. . . Section board

138. . . Air section

140. . . Flue gas section

142. . . Heat exchange element

144. . . Cold end

146. . . Hot end

148. . . boiler

152. . . Baffle assembly

154. . . Flue gas duct

156. . . Baffle

158. . . Controller

160. . . Power plant distributed control system

162. . . Baffle assembly

163. . . Baffle panel

164. . . Baffle panel

166. . . Actuator

168. . . driver

174. . . Part of the flue gas inlet 124

178. . . Rod seal

179. . . Rod seal

182. . . frame

188. . . fan

224. . . Flue gas flow

226. . . Flue gas flow

230. . . Air inlet flow

232. . . Heated air outlet flow

Figure 1 is a partial perspective, cross-sectional view of a conventional rotary regenerative air preheater;

Figure 2 is a schematic illustration of a vapor generation system having a regenerative air preheater configuration in accordance with the present invention;

Figure 3 is a side perspective view of the baffle manifold of Figure 2;

Figure 4 is a top plan view of the baffle manifold of Figure 3;

Figure 5 is a cross-sectional view taken along line V-V of Figure 3;

Figure 6 is an enlarged view of a region VI of Figure 5.

152. . . Baffle assembly

156. . . Baffle

162. . . Baffle assembly

163. . . Baffle panel

164. . . Baffle panel

166. . . Actuator

168. . . driver

182. . . frame

Claims (15)

An air preheater having a flue gas inlet for receiving flue gas from a boiler, a flue gas outlet for exhausting flue gas, and an air inlet for receiving air for preheating and The air preheater for providing preheated air to an air outlet of the boiler and exhibiting reduced fouling at various boiler operating levels includes: an air baffle assembly adapted to adjust the air One of the inlet openings, the air baffle assembly being tightly fitted against the air inlet to minimize air leakage between the baffle assembly and the air inlet; a flue gas baffle assembly adapted To adjust an opening of the flue gas inlet, the flue gas baffle assembly closely fits against the flue gas inlet to minimize one of the flue gas baffle assembly and the flue gas inlet Air leakage; a controller coupled to the air baffle assembly and the flue gas baffle assembly, based on a signal provided by a boiler through a distributed control system, the controller being adapted to be different Operating the air baffle assembly during boiler operating level The flue gas baffle assembly to maintain a desired air velocity and gas flow rate to reduce fouling; and wherein the baffle assembly reduces the flue gas inlet flow area to significantly increase the flue gas flow The velocity is to erode the fly ash deposited on the heat exchange element of the air preheater, and wherein the rate of erosion is proportional to the speed at which one of the specific agents is a power. The air preheater of claim 1, wherein the controller is adapted to receive input regarding the operating level of the boiler and to each other based on the received input At least one of the flue gas baffle assembly and the air baffle assembly is operatively controlled. The air preheater of claim 1, wherein the controller is adapted to receive an input of a temperature of the flue gas exiting the flue gas outlet and interactively control the flue gas baffle based on the received input And forming at least one of the air baffle assemblies. The air preheater of claim 1, wherein the controller is adapted to receive an input of a velocity of the flue gas exiting the flue gas outlet and interactively control the flue gas barrier based on the received input At least one of the plate assembly and the air baffle assembly. The air preheater of claim 1, wherein the controller is adapted to: receive an input regarding a maximum allowable flue gas outlet temperature; measure a temperature of a flue gas outlet stream; and control the flue gas baffle At least one of the assembly and the air baffle assembly to maximize velocity of air entering the air inlet while maintaining the measured temperature of the flue gas outlet flow below the maximum allowable smoke Road temperature. The air preheater of claim 1, wherein the controller is adapted to receive an input regarding the flue gas exit velocity and interactively control the flue gas baffle assembly and the air block based on the received input At least one of the board assemblies. The air preheater of claim 1, wherein the controller is further adapted to adjust the flue gas baffle assembly and the air baffle assembly to reduce the amount of acid condensate in the air preheater . The air preheater of claim 1, wherein the air baffle assembly comprises: a plurality of baffles adapted to adjustably close at least a portion of the air inlet. The air preheater of claim 1, wherein the flue gas baffle assembly comprises: a plurality of baffles adapted to adjustably close at least a portion of the flue gas inlet. The air preheater of claim 1, wherein the baffles are pivotable and pivoted by a drive rod attached to one of the baffles. The air preheater of claim 10, wherein the actuator moves the drive rod to cause the flaps to pivot. A method of reducing fouling of an air preheater having an air inlet and a flue gas inlet during a cycle of reducing boiler operation, comprising the steps of: measuring one of flue gas outlet streams exiting the preheater Determining whether the measured gas outlet temperature is below a predetermined threshold; and when the measured temperature is below the predetermined threshold, calculating to close at least one of the flue gas inlet and the air inlet An amount to increase the temperature of the flue gas outlet stream to be above the threshold temperature; and to close the smoke in the calculated amount when the measured gas outlet stream temperature is below the predetermined threshold a gas inlet and the air inlet to cause an increase in the temperature of the flue gas outlet stream, thereby reducing acid condensation and fouling, wherein closing the flue gas inlet and the air inlet includes reducing the flue a gas inlet flow area to significantly increase the flue gas flow rate to erode fly ash deposited on the heat exchange element of the air preheater, and wherein the erosion rate is at a rate that is greater than a specific power for an etchant proportion. A method of reducing fouling according to claim 12, wherein the predetermined threshold temperature is present in a condensation temperature of one of the flue gases plus a safety margin. A method of reducing fouling of one of an air preheater having an air inlet and a flue gas inlet during a cycle of reducing boiler operation, comprising the steps of: measuring the flue gas passing through the preheater and a speed of at least one of the air; determining a difference between the measured speed and a desired speed; calculating an amount to adjust at least one of a flue gas inlet opening and an air inlet opening to a minimum Differentiating between the measured speed and the desired speed; adjusting at least one of the flue gas inlet and the air inlet opening by the calculated amount, resulting in an adjusted exit speed, thereby increasing to any Erosion of aggregates and scales, and wherein the rate of erosion is proportional to the speed at which one of the specific agents is a power. The method of reducing fouling of claim 14, further comprising the steps of: receiving a maximum flue gas outlet stream temperature; measuring a flue gas outlet stream temperature; and limiting the step of adjusting to ensure the measured flue gas The outlet stream temperature is below the maximum flue gas outlet stream temperature.