Not able to draw the images inside large excel file in batches

Actually, I am generating a large excel file with image's urls and after that I try to draw the images (in batches) in a column (Column 1 with blank entries) using image url (Column 2 with image url) in that generated file. Here first batch of images draw the images successfully in excel file, when second batch of images start their process to draw the images, it's also draw the images successfully but during this process, images drawn by first batch are removed from excel file. I am using cron job to draw the images in batches inside excel file.

My question is that why images drawn by previous batches removes from the excel file, after completing the image draw process, it's showing images of last batch only inside excel file.

Process:

1. I have generated an excel file (xyz_file.xlsx) with 10000 of records.
2. There is also an column for image url's and a blank column for images in generated excel file.
3. I get all image urls column values and keep in an array (with 10000 image urls) from generated excel file.
4. I divide the image urls into 10 batches of 1000 records in each batch.
5. I try to draw the images one by one batches.

Please explain me why it's not keeping the image records drawn by previous batches inside excel file. Where am I doing wrong. How can I solve it?

Thanks in advance.