阅读说明：本技术 一种三氟化氮电解槽的加料系统和方法 (Charging system and method for nitrogen trifluoride electrolytic cell ) 是由 纪振红 马朝选 王振宇 郑阳光 赵志刚 乔蓓蓓 王军岭 宋忠华 于 2020-12-22 设计创作，主要内容包括：本发明公开了一种三氟化氮电解槽的加料系统,沿氨的流向依次连接液氨储罐、氨汽化器、氨气缓冲罐、分子筛塔、第一过滤器、止回阀,最后接入氨气主管路；沿HF的流向依次连接HF储罐、HF汽化器、HF缓冲罐、第二过滤器,最后接入HF主管路；电解槽中设置有液位计和密度计；电解槽与氨气主管路和HF主管路的连接管路上连接有电解槽流量计和用于控制电解槽中氨气/HF比例的电解槽通入流量阀门；所述电解槽通入流量阀门和所述液位计构成液位连锁控制环路,与所述密度计构成成分比例控制环路；控制器连接各个传感器和阀门。本发明还基于该装置提供了一种加料方法。使用本发明能够提高补料操作的安全性,提高电解槽产气收集率,降低设备和人员成本。(The invention discloses a feeding system of a nitrogen trifluoride electrolytic cell, which is sequentially connected with a liquid ammonia storage tank, an ammonia vaporizer, an ammonia buffer tank, a molecular sieve tower, a first filter and a check valve along the flow direction of ammonia, and finally connected into an ammonia main pipeline; the HF storage tank, the HF vaporizer, the HF buffer tank and the second filter are sequentially connected along the flow direction of HF, and finally the HF storage tank, the HF vaporizer, the HF buffer tank and the second filter are connected to an HF main pipeline; a liquid level meter and a density meter are arranged in the electrolytic tank; the connecting pipeline of the electrolytic cell, the ammonia gas main pipeline and the HF main pipeline is connected with an electrolytic cell flowmeter and an electrolytic cell inlet flow valve for controlling the proportion of ammonia gas/HF in the electrolytic cell; the electrolytic cell is communicated with a flow valve and the liquid level meter to form a liquid level interlocking control loop, and the electrolytic cell and the densimeter form a component proportion control loop; the controller is connected with each sensor and the valve. The invention also provides a feeding method based on the device. The invention can improve the safety of material supplementing operation, improve the gas production collection rate of the electrolytic cell and reduce the cost of equipment and personnel.)

1. A feed system for a nitrogen trifluoride electrolyzer, characterized by comprising:

a liquid ammonia storage tank, an ammonia vaporizer, an ammonia buffer tank, a molecular sieve tower, a first filter and a check valve are sequentially connected along the flow direction of ammonia, and finally, the liquid ammonia is connected to an ammonia main pipeline; the ammonia buffer tank is provided with a first pressure gauge, and a first pressure interlocking valve for controlling the air inlet flow rate of the ammonia buffer tank is connected to a pipeline between the liquid ammonia storage tank and the ammonia vaporizer; the first pressure interlocking valve and the first pressure gauge are both connected with a controller to form an ammonia buffer tank pressure interlocking control loop; an ammonia flow valve for controlling the ammonia flow in the ammonia main pipeline and an ammonia flow meter for detecting the ammonia flow in the ammonia main pipeline are arranged on a pipeline between the check valve and the ammonia main pipeline; the ammonia flow valve and the ammonia flow meter are both connected with a controller to form an ammonia total flow interlocking control loop;

the HF storage tank, the HF vaporizer, the HF buffer tank and the second filter are sequentially connected along the flow direction of the hydrogen fluoride HF, and finally the HF storage tank, the HF vaporizer, the HF buffer tank and the second filter are connected to an HF main pipeline; the HF buffer tank is provided with a second pressure gauge, and a second pressure interlocking valve for controlling the air inlet flow rate of the HF buffer tank is connected to a pipeline between the HF storage tank and the HF vaporizer; the second pressure interlocking valve and the second pressure gauge are both connected with the controller to form an HF buffer tank pressure interlocking control loop; an HF flow valve for controlling HF flow in the HF main pipeline and an HF flow meter for detecting the HF flow in the HF main pipeline are arranged on a pipeline between the second filter and the HF main pipeline; the HF flow valve and the HF flowmeter are both connected with the controller to form an HF total flow linkage control loop;

a plurality of electrolytic tanks are connected in parallel and are respectively connected into the ammonia gas main pipeline and the HF main pipeline; a liquid level meter and a density meter are arranged in the electrolytic tank; the connecting pipeline of the electrolytic cell and the ammonia main pipeline and the connecting pipeline of the electrolytic cell and the HF main pipeline are both connected with an electrolytic cell flowmeter and an electrolytic cell lead-in flow valve for controlling the proportion of ammonia gas/HF entering the electrolytic cell; the electrolytic bath inlet flow valve and the liquid level meter are both connected with a controller to form a liquid level interlocking control loop; the densimeter is also connected with the controller and forms a component proportion control loop with the flow valve introduced into the electrolytic cell;

the liquid ammonia storage tank with the output pipeline of HF storage tank all links there is the delivery pump, and the delivery pump is connected the controller.

2. The system of claim 1, wherein the molecular sieve column comprises a 2-stage molecular sieve column.

3. The system of claim 1, wherein the molecular sieve column comprises two primary and secondary sets of molecular sieve columns in parallel.

4. The system of claim 1, wherein the first filter and the second filter each comprise two stages of filters in series, a coarse filter and a fine filter.

5. The system of claim 1, wherein a valve is provided between each two devices for shutting down when repairing or replacing the devices.

6. The system of claim 1, wherein the cell includes a temperature sensor and a heating device, each operatively connected to the controller, to control the cell temperature to between 80 ℃ and 130 ℃.

7. The system of claim 1, wherein the cell pressure is atmospheric.

8. A method of charging a nitrogen trifluoride electrolysis cell, characterized by using a system according to any one of claims 1 to 7; the method comprises the following steps:

step 1, respectively starting the delivery pumps of an HF storage tank and a liquid ammonia storage tank, and controlling the outlet flow of the delivery pumps;

step 2, after the liquid ammonia is converted into ammonia gas by an ammonia vaporizer, the ammonia gas passes through an ammonia gas buffer tank, a molecular sieve tower, a first filter and a check valve and then enters an ammonia gas main pipeline under the control of the flow of an ammonia gas flow valve; HF is converted into HF gas by an HF vaporizer, and then enters an HF main pipeline under the flow control of an HF flow valve after passing through an HF buffer tank and a second filter;

the controller controls the air inlet flow rates of the HF buffer tank and the ammonia buffer tank according to the acquisition values of the first pressure gauge and the second pressure gauge;

step 3, controlling the total flow of ammonia and HF by controlling the opening of an ammonia flow valve and an HF flow valve by a controller according to the acquisition values of the ammonia flow meter and the HF flow meter;

step 4, the controller controls the electrolytic cell to be introduced into the flow valve according to the acquisition value of the liquid level meter to realize the liquid supplement of the electrolytic cell; when the liquid level is supplemented to a required value, automatically closing the flow valve for introducing the electrolytic cell, and when the liquid level is lower than the required value, controlling the flow valve for introducing the electrolytic cell to open and supplement the electrolyte;

the controller also obtains the ratio of HF to ammonia in the electrolyte according to the acquisition value of the densimeter in the electrolytic cell, compares the ratio with the required ratio, and realizes the adjustment of the ratio of the ammonia gas to the HF by controlling the opening of the flow valve which is communicated with the electrolytic cell.

9. The method of claim 8, further comprising: and the controller outputs the acquired values of the ammonia gas flowmeter, the HF flowmeter, the electrolytic bath flowmeter and the liquid level meter to a display for displaying.

Technical Field

The invention relates to the technical field of nitrogen trifluoride preparation, in particular to a feeding system and a feeding method of a nitrogen trifluoride electrolytic cell.

Background

Nitrogen trifluoride is a colorless, odorless and stable gas at normal temperature, is a strong oxidant, is used as an excellent plasma etching gas in the microelectronic industry, is cracked into active fluorine ions during ion etching, has excellent etching rate and selectivity (for silicon oxide and silicon) for silicon and tungsten compounds, is a very good cleaning agent for high-purity nitrogen trifluoride, does not leave any residue on the surface of an etching object during etching, and is widely applied to chip manufacturing and high-energy lasers. With the development of nanotechnology and the large-scale development of technology in the electronics industry, the demand for it will increase.

Although nitrogen trifluoride is a low toxic substance, it can strongly irritate the eye, skin and respiratory mucosa, eroding tissues. Inhalation of high concentrations of NF3 can cause headache, vomiting and diarrhea. Long term inhalation of low concentration NF₃Can damage teeth and bones, and make teeth yellow spots and bones deformed. Has strong oxidizing property. Can react with the reducing agent strongly to cause combustion explosion.

In the preparation of nitrogen trifluoride, the electrolysis bath needs to be charged for convenient preparation. If adopt artifical reinforced mode, the cost of labor is high, can not guarantee personnel's safety, and influences machining efficiency. For the automatic feeding scheme, the existing scheme firstly adopts a tank body to mix ammonia and Hydrogen Fluoride (HF) to form a mixed solution, and then the mixed solution is added into an electrolytic tank through a pipeline. The transmission of liquid has high requirements on pipelines and high cost. And the scheme of mixing firstly is the same for the proportion of the materials introduced into different electrolytic tanks, and the materials cannot be configured according to the direct electrolysis effect, so that the gas production collection rate can be reduced, and the processing efficiency can be influenced.

Disclosure of Invention

In view of the above, the present invention provides a feeding system and method for a nitrogen trifluoride electrolyzer, which can improve the safety of feeding operation, improve the yield of gas produced by the electrolyzer, and reduce the cost of equipment and personnel.

In order to solve the above-mentioned technical problems, the present invention has been accomplished as described above.

A feed system for a nitrogen trifluoride electrolyzer, comprising:

a liquid ammonia storage tank, an ammonia vaporizer, an ammonia buffer tank, a molecular sieve tower, a first filter and a check valve are sequentially connected along the flow direction of ammonia, and finally, the liquid ammonia is connected to an ammonia main pipeline; the ammonia buffer tank is provided with a first pressure gauge, and a first pressure interlocking valve for controlling the air inlet flow rate of the ammonia buffer tank is connected to a pipeline between the liquid ammonia storage tank and the ammonia vaporizer; the first pressure interlocking valve and the first pressure gauge are both connected with a controller to form an ammonia buffer tank pressure interlocking control loop; an ammonia flow valve for controlling the ammonia flow in the ammonia main pipeline and an ammonia flow meter for detecting the ammonia flow in the ammonia main pipeline are arranged on a pipeline between the check valve and the ammonia main pipeline; the ammonia flow valve and the ammonia flow meter are both connected with a controller to form an ammonia total flow interlocking control loop;

the HF storage tank, the HF vaporizer, the HF buffer tank and the second filter are sequentially connected along the flow direction of the hydrogen fluoride HF, and finally the HF storage tank, the HF vaporizer, the HF buffer tank and the second filter are connected to an HF main pipeline; the HF buffer tank is provided with a second pressure gauge, and a second pressure interlocking valve for controlling the air inlet flow rate of the HF buffer tank is connected to a pipeline between the HF storage tank and the HF vaporizer; the second pressure interlocking valve and the second pressure gauge are both connected with the controller to form an HF buffer tank pressure interlocking control loop; an HF flow valve for controlling HF flow in the HF main pipeline and an HF flow meter for detecting the HF flow in the HF main pipeline are arranged on a pipeline between the second filter and the HF main pipeline; the HF flow valve and the HF flowmeter are both connected with the controller to form an HF total flow linkage control loop;

a plurality of electrolytic tanks are connected in parallel and are respectively connected into the ammonia gas main pipeline and the HF main pipeline; a liquid level meter and a density meter are arranged in the electrolytic tank; the connecting pipeline of the electrolytic cell and the ammonia main pipeline and the connecting pipeline of the electrolytic cell and the HF main pipeline are both connected with an electrolytic cell flowmeter and an electrolytic cell lead-in flow valve for controlling the proportion of ammonia gas/HF entering the electrolytic cell; the electrolytic bath inlet flow valve and the liquid level meter are both connected with a controller to form a liquid level interlocking control loop; the densimeter is also connected with the controller and forms a component proportion control loop with the flow valve introduced into the electrolytic cell;

the liquid ammonia storage tank with the output pipeline of HF storage tank all links there is the delivery pump, and the delivery pump is connected the controller.

Preferably, the molecular sieve column comprises a 2-stage molecular sieve column.

Preferably, the molecular sieve tower comprises a main molecular sieve tower and a standby molecular sieve tower which are connected in parallel.

Preferably, the first filter and the second filter each comprise two stages of filters in series, namely a coarse filter and a fine filter.

Preferably, a valve which is used for shutting off when the device is repaired or replaced is arranged between every two devices in the system.

Preferably, the electrolytic cell comprises a temperature sensor and a heating device which are connected with a controller to work, and the temperature of the electrolytic cell is controlled to be 80-130 ℃.

Preferably, the cell pressure is atmospheric.

The invention provides a feeding method of a nitrogen trifluoride electrolytic cell, which adopts any one system; the method comprises the following steps:

step 1, respectively starting the delivery pumps of an HF storage tank and a liquid ammonia storage tank, and controlling the outlet flow of the delivery pumps;

step 2, after the liquid ammonia is converted into ammonia gas by an ammonia vaporizer, the ammonia gas passes through an ammonia gas buffer tank, a molecular sieve tower, a first filter and a check valve and then enters an ammonia gas main pipeline under the control of the flow of an ammonia gas flow valve; HF is converted into HF gas by an HF vaporizer, and then enters an HF main pipeline under the flow control of an HF flow valve after passing through an HF buffer tank and a second filter;

the controller controls the air inlet flow rates of the HF buffer tank and the ammonia buffer tank according to the acquisition values of the first pressure gauge and the second pressure gauge;

step 3, controlling the total flow of ammonia and HF by controlling the opening of an ammonia flow valve and an HF flow valve by a controller according to the acquisition values of the ammonia flow meter and the HF flow meter;

step 4, the controller controls the electrolytic cell to be introduced into the flow valve according to the acquisition value of the liquid level meter to realize the liquid supplement of the electrolytic cell; when the liquid level is supplemented to a required value, automatically closing the flow valve for introducing the electrolytic cell, and when the liquid level is lower than the required value, controlling the flow valve for introducing the electrolytic cell to open and supplement the electrolyte;

the controller also obtains the ratio of HF to ammonia in the electrolyte according to the acquisition value of the densimeter in the electrolytic cell, compares the ratio with the required ratio, and realizes the adjustment of the ratio of the ammonia gas to the HF by controlling the opening of the flow valve which is communicated with the electrolytic cell.

Preferably, the method further comprises: and the controller outputs the acquired values of the ammonia gas flowmeter, the HF flowmeter, the electrolytic bath flowmeter and the liquid level meter to a display for displaying.

Has the advantages that:

(1) the invention vaporizes liquid ammonia and liquid HF into ammonia gas and HF gas, which are transmitted to each electrolytic tank through pipelines. The gas transmission has relatively lower pipeline requirements than liquid and higher safety, thereby reducing the equipment cost and the requirements on personnel. Meanwhile, the two substances are respectively transmitted to the electrolytic tanks through pipelines, so that the flow of the two substances can be respectively controlled, the proportion can be adjusted according to the density of the electrolyte, and the gas production collection rate is improved.

(2) Under the condition that the electrolytic cell continuously generates nitrogen trifluoride, hydrogen fluoride and ammonia gas are added into the electrolytic cell through pipelines by using a delivery pump, so that continuous feeding and proportion adjustment of the electrolytic cell are realized.

(3) The electrolytic cell utilizes the pipeline to continuously feed, can improve the safety of feeding operation, improve the yield of the produced gas of the electrolytic cell, reduce the personnel cost, can prepare NF3 gas safely on a large scale, and has strong practicability.

Drawings

FIG. 1 is a schematic diagram of the composition of the feed system of the nitrogen trifluoride electrolyzer of the present invention.

Detailed Description

The invention is described in detail below by way of example with reference to the accompanying drawings.

Referring to FIG. 1, the present invention provides a feed scheme for nitrogen trifluoride electrolyzers that vaporizes liquid ammonia and liquid HF into ammonia and HF gases for separate delivery to each electrolyzer via lines. The gas transmission has relatively lower pipeline requirements than liquid and higher safety, thereby reducing the equipment cost and the requirements on personnel. Meanwhile, the two substances are respectively transmitted to the electrolytic tanks through pipelines, so that the flow of the two substances can be respectively controlled, the proportion can be adjusted according to the density of the electrolyte, and the gas production collection rate is improved.

FIG. 1 is a feed system for a nitrogen trifluoride electrolyzer of the invention, as shown in FIG. 1:

for the ammonia feed line: connect gradually liquid ammonia storage tank, ammonia vaporizer, ammonia buffer tank, molecular sieve tower, first filter, check valve along the flow direction of ammonia, insert the ammonia main line at last.

The output pipeline of the liquid ammonia storage tank is connected with a delivery pump for controlling the outlet flow of the liquid ammonia and ensuring the continuous feeding of the electrolytic tank. The delivery pump is connected with the controller.

The ammonia buffer tank is provided with a first pressure gauge, and a first pressure interlocking valve for controlling the air inlet flow rate of the ammonia buffer tank is connected to a pipeline between the liquid ammonia storage tank and the ammonia vaporizer; the first pressure interlocking valve and the first pressure gauge are both connected with the controller to form an ammonia buffer tank pressure interlocking control loop. A pressure value, for example, 0.3MP, may be preset, and the controller may control the flow rate of the ammonia buffer tank inlet air by adjusting the opening degree of the first pressure interlock valve according to the collected value of the first pressure gauge, so as to keep the pressure of the ammonia buffer tank at about 0.3 MP. By using the better pressure, the continuous feeding of the electrolytic cell is ensured.

The molecular sieve tower is used for filtering heavy oil in liquid ammonia, and comprises a 2-stage molecular sieve tower in a preferred embodiment; meanwhile, two sets of main and standby molecular sieve towers which are connected in parallel can be arranged, and the two sets of molecular sieve towers are switched by a valve. When the molecular sieve tower of the main part needs to be overhauled or maintained, the molecular sieve tower is switched to the backup molecular sieve tower, and vice versa.

The first filter is used for filtering particulate impurities and residual oil. In the preferred embodiment, the first filter comprises two stages of filters connected in series, and is divided into a coarse filter and a fine filter, wherein the coarse filter is performed first, and the fine filter is performed first.

And an ammonia flow valve for controlling the ammonia flow in the ammonia main pipeline and an ammonia flow meter for detecting the ammonia flow in the ammonia main pipeline are arranged on a pipeline between the check valve and the ammonia main pipeline. The ammonia flow valve and the ammonia flow meter are both connected with the controller to form an ammonia total flow interlocking control loop. The controller can adjust the opening of the ammonia flow valve according to the acquisition value of the ammonia flowmeter so as to control the ammonia gas supply flow.

For the feed line for HF: the HF storage tank, the HF vaporizer, the HF buffer tank and the second filter are sequentially connected along the flow direction of the hydrogen fluoride HF, and finally the HF storage tank, the HF vaporizer, the HF buffer tank and the second filter are connected to an HF main pipeline.

The output pipeline of the HF storage tank is connected with a delivery pump for controlling the outlet flow of HF and ensuring the continuous feeding of the electrolytic bath. The delivery pump is connected with the controller.

The HF buffer tank is provided with a second pressure gauge, and a second pressure interlocking valve for controlling the air inlet flow rate of the HF buffer tank is connected to a pipeline between the HF storage tank and the HF vaporizer; the second pressure interlocking valve and the second pressure gauge are both connected with the controller to form an HF buffer tank pressure interlocking control loop. A pressure value can be preset, and the controller can control the air inlet flow rate of the HF buffer tank by adjusting the opening degree of the second pressure linkage valve according to the acquisition value of the second pressure gauge, so that the pressure of the HF buffer tank is kept at about a set value.

In the preferred embodiment, the second filter comprises two stages of filters connected in series, and is divided into a coarse filter and a fine filter, wherein the coarse filter is performed first, and the fine filter is performed later.

An HF flow valve for controlling HF flow in the HF main pipeline and an HF flow meter for detecting the HF flow in the HF main pipeline are arranged on a pipeline between the second filter and the HF main pipeline; the HF flow valve and the HF flowmeter are both connected with the controller to form an HF total flow interlocking control loop. The controller can adjust the opening of the HF flow valve according to the acquisition value of the HF flowmeter so as to control the HF gas supply flow.

The system comprises a plurality of electrolytic cells which are connected in parallel and are respectively connected into an ammonia main pipeline and an HF main pipeline. A liquid level meter and a density meter are arranged in each electrolytic cell. The connecting pipeline of the electrolytic cell and the ammonia main pipeline and the connecting pipeline of the HF main pipeline are both connected with an electrolytic cell flowmeter and an electrolytic cell lead-in flow valve. The cell inlet flow valve is used to control the flow of ammonia/HF into the cell and thus the ammonia/HF ratio into the cell.

The electrolytic cell is connected with the controller through the flow valve and the liquid level meter to form a liquid level interlocking control loop. And the controller controls the flow valve to be introduced into the electrolytic cell according to the acquired value of the liquid level meter to realize liquid supplement of the electrolytic cell, automatically closes the flow valve to be introduced into the electrolytic cell when the liquid level is supplemented to a required value, and automatically opens and supplements electrolyte when the liquid level is lower than the required value.

The electrolytic cell inlet flow valve and the densimeter are both connected with the controller to form a component proportion control loop. The controller obtains the ratio of HF to ammonia in the electrolyte according to the acquisition value of the densimeter, compares the ratio with the required ratio to determine the introduction amount of ammonia and HF, and realizes the ratio adjustment of the ammonia and the HF by controlling the opening of the inlet flow valve of the electrolytic cell.

The electrolytic bath can also be provided with a temperature sensor and a heating device which are connected with the controller to work, and the temperature of the electrolytic bath is controlled to be 80-130 ℃. The pressure of the electrolytic cell is normal pressure. The liquid level height of the electrolytic cell can be controlled to be 550 mm.

Valves which are used for shutting off when the devices are maintained and replaced can be arranged between every two devices in the system. The valves can be manually controlled or can be automatically controlled by connecting with a controller. When a certain device needs to be maintained, the valves at the two ends of the device are closed, and after the device is maintained or replaced, the valves at the two ends of the device are opened.

The controller can also be connected with a display to output the acquisition values of the ammonia gas flowmeter, the HF flowmeter, the ammonia gas pipeline and the electrolytic bath flowmeter and the liquid level meter of the HF pipeline to the display for displaying.

The feeding method of the nitrogen trifluoride electrolytic cell feeding system comprises the following steps:

step 1, respectively starting the delivery pumps of an HF storage tank and a liquid ammonia storage tank, and controlling the outlet flow of the delivery pumps;

step 2, after the liquid ammonia is converted into ammonia gas by an ammonia vaporizer, the ammonia gas passes through an ammonia gas buffer tank, a molecular sieve tower, a first filter and a check valve and then enters an ammonia gas main pipeline under the control of the flow of an ammonia gas flow valve; HF is converted into HF gas by an HF vaporizer, and then enters an HF main pipeline under the flow control of an HF flow valve after passing through an HF buffer tank and a second filter;

the controller controls the air inlet flow rates of the hydrogen fluoride and the ammonia gas entering the buffer tank through the pressure interlocking of the buffer tanks according to the acquisition values of the first pressure gauge and the second pressure gauge;

step 3, controlling the total flow of ammonia and HF by controlling HF of the ammonia flow valve and the HF flow valve by the controller according to the acquisition values of the ammonia flow meter and the HF flow meter;

step 4, the controller controls the electrolytic cell to be introduced into the flow valve to realize liquid supplement of the electrolytic cell according to the acquired value of the liquid level meter, automatically closes the electrolytic cell to be introduced into the flow valve when the liquid level is supplemented to a required value, and controls the electrolytic cell to be introduced into the flow valve to open and supplement electrolyte when the liquid level is lower than the required value;

the controller also obtains the ratio of HF to ammonia in the electrolyte according to the acquisition value of the densimeter in the electrolytic cell, compares the ratio with the required ratio, and adjusts the ratio of the ammonia to the HF by controlling the opening of the flow valve which is communicated into the electrolytic cell so as to enable the ratio to meet the set requirement.

And 5, outputting the acquired values of the ammonia gas flowmeter, the HF flowmeter, the electrolytic cell flowmeter of the ammonia gas pipeline, the electrolytic cell flowmeter of the HF pipeline and the liquid level meter to a display by the controller for displaying.

The above embodiments only describe the design principle of the present invention, and the shapes and names of the components in the description may be different without limitation. Therefore, a person skilled in the art of the present invention can modify or substitute the technical solutions described in the foregoing embodiments; such modifications and substitutions do not depart from the spirit and scope of the present invention.